Identification of cellular mechanisms operational in vivo during the regression of established pulmonary metastases by the systemic administration of high-dose recombinant interleukin 2

The systemic administration of high-dose recombinant IL 2 mediated significant reductions of established 3-day pulmonary micrometastases from both weakly immunogenic and nonimmunogenic sarcomas. However, when treatment with IL 2 was delayed for 10 days after the injection of tumor cells in an attempt to treat grossly visible pulmonary macrometastases, only those established from weakly immunogenic sarcomas remained susceptible. Established 10-day pulmonary nodules from the nonimmunogenic sarcomas became refractory to IL 2 therapy. We utilized selective depletion of lymphocyte subsets in vivo by the systemic administration of specific monoclonal antibodies to cells bearing either the L3T4 or Lyt-2 marker or a heteroantiserum to cells bearing the ASGM-1 glycosphingolipid to identify lymphocytes involved in IL 2-induced tumor regression. Cells with potent lymphokine-activated killer (LAK) activity against fresh tumor targets in vitro were identified in the lungs of IL 2-treated mice. By flow cytometry analysis, the majority of these effector cells were Thy-1+, L3T4-, Lyt-2-, ASGM-1+. Depletion in vivo of ASGM-1+ cells before the onset of IL 2 administration eliminated the successful therapy of 3-day pulmonary metastases from nonimmunogenic sarcomas, with concurrent elimination of LAK cell activity in the lungs. In mice with 3-day pulmonary metastases from weakly immunogenic sarcomas, both Lyt-2+ cells and ASGM-1+ cells were involved in IL 2-mediated tumor regression, but Lyt-2+ cells appeared to be the more potent mediator in the response. Lyt-2+ cells were also involved in the elimination of grossly visible 10-day macrometastases from these weakly immunogenic tumors. Depletion of L3T4+ cells had no effect on tumor regression. Thus, although LAK effectors derived from ASGM-1+ precursors can eliminate pulmonary micrometastases regardless of tumor immunogenicity, Lyt-2+ cells are predominant effectors in the elimination of both pulmonary micro- and macrometastases from weakly immunogenic sarcomas.     

Adoptive immunotherapy of murine hepatic metastases with lymphokine activated killer (LAK) cells and recombinant interleukin 2 (RIL 2) can mediate the regression of both immunogenic and nonimmunogenic sarcomas and an adenocarcinoma

The incubation of normal murine splenocytes in recombinant interleukin 2 (RIL 2) gives rise to lymphokine-activated killer (LAK) cells that are specifically cytotoxic to fresh noncultured, autologous, syngeneic, and allogeneic primary and metastatic tumor cells, but are not toxic to normal cells. We have recently shown that the systemic injection of RIL 2 given alone or in conjunction with LAK cells can reduce the number of established pulmonary and hepatic micrometastases from a weakly immunogenic sarcoma in mice. In this report we have analyzed the response of hepatic metastases (HM) induced from both a nonimmunogenic sarcoma (MCA-102) and an adenocarcinoma (MCA-38). Treatment of mice bearing HM from the MCA-102 and MCA-38 tumors revealed that low doses of RIL 2 (5000 to 25,000 U t.i.d.) had little if any anti-tumor effect when given alone (mean percent reduction over control for the MCA-102 tumor: 14%, for the MCA-38 tumor: 10%, p, not significant). Doses of 100,000 U of RIL 2 affected a 38 and 53% reduction in the number of metastases over control for the MCA-102 and MCA-38 tumors, respectively (p less than 0.05). However, when LAK cells were added to the same doses of RIL 2, the corresponding mean percent reduction over control was 90% (p less than 0.005) and 61% (p less than 0.05) for MCA-102 and MCA-38, respectively, at RIL 2 doses of 5000 to 25,000 t.i.d. At doses of 100,000 U of RIL 2 administered with LAK cells, the corresponding percent reductions were 98 and 99%, respectively (p less than 0.005). Therapy with LAK cells plus RIL 2 can also prolong the survival of these mice. In addition, the intraportal administration of LAK cells is more effective than the i.v. administration of these cells. Thus, treatment of established HM from a nonimmunogenic sarcoma and an adenocarcinoma can be successfully mediated by the systemic infusion of LAK cells with RIL 2. These findings provide a rationale for clinical trials of infusion of LAK cells with RIL 2 in the therapy of HM in humans.     

Antibody-dependent cellular cytotoxicity mediated by murine lymphocytes activated in recombinant interleukin 2

The incubation of murine splenocytes in recombinant interleukin 2 (RIL 2) gives rise to lymphokine-activated killer (LAK) cells that can lyse fresh, NK-resistant tumor cells but not normal cells in 4-hr 51Cr-release assays. Lysis by this IL 2-activated cell population was enhanced up to 100-fold by prior reaction of target cells with specific antisera reactive with antigens on the target cells. This antibody-dependent cellular cytotoxicity (ADCC) also resulted in lysis of fresh normal target cells, which are not usually susceptible to LAK lysis. The ADCC was evident after 24 hr of incubation of splenocytes in RIL 2, but peak lytic activity was reached after 3 to 4 days of incubation. The concentrations of RIL 2 needed for the in vitro activation of the effectors in order to attain maximal ADCC was between 100 and 3000 U/ml and parallel the IL 2 concentrations required to generate LAK cells. ADCC mediated by IL 2-activated splenocytes was completely blocked by anti-FcR monoclonal antibodies. Although antisera directed against MHC antigens were used in most experiments, anti-B16 monoclonal antibodies have also shown the ability to induce ADCC mediated by RIL 2-activated syngeneic and allogeneic cells. Treatment of the precursor splenocyte populations with anti-asialo GM1 and complement eliminated the direct LAK activity and the antibody-dependent cytotoxicity, suggesting that both direct and indirect tumor cell lysis may be caused by the same effector cell. ADCC mediated by LAK cell populations represents another possible mechanism for the in vivo therapeutic effects of these cells.     

Recombinant interleukin 2 stimulates in vivo proliferation of adoptively transferred lymphokine-activated killer (LAK) cells

We previously reported that the adoptive transfer of lymphokine-activated killer (LAK) cells plus repetitive injections of recombinant interleukin 2 (IL 2) produced a marked reduction in established pulmonary metastases from a variety of murine sarcomas. The requirement for the exogenous administration of IL 2 prompted a subsequent examination of the role of IL 2 in the in vivo function of transferred LAK cells. The in vivo proliferation and migration patterns of lymphoid cells in C57BL/6 mice were examined after i.v. transfer of LAK cells alone, i.p. injection of IL 2 alone, or the combination of LAK cells and IL 2. A model for in vivo labeling of the DNA of dividing cells was used in which mice were injected with 5-[125I]-iodo-2'-deoxyuridine (125IUdR) and, 20 hr later, their tissues were removed and were counted in a gamma analyzer. A proliferation index (PI) was calculated by dividing the mean cpm of organs of experimentally treated mice by the mean cpm of organs of control mice. In animals given LAK cells alone, the lungs and liver demonstrated little if any uptake of 125IUdR above saline-treated controls (PI = 2.5 and 0.8, respectively, on day 5), whereas the same organs of mice receiving 6000 U of IL 2 alone displayed higher radiolabel incorporation (PI = 7.1 and 5.9, respectively). When mice were given LAK cells plus 6000 U of IL 2, their tissues showed an additional increase in 125IUdR uptake. In the spleen, kidneys, and mesenteric lymph nodes, IL 2 treatment alone (6000 U) produced elevated PI values that were not, however, additionally increased if LAK cells were also administered. To separate the stimulatory effects of IL 2 on host lymphocyte proliferation from similar IL 2 effects on injected LAK cells, these studies were repeated in mice immunosuppressed by 500 rad total body irradiation. Pre-irradiation of the host sufficiently reduced endogenous lymphoid expansion stimulated by IL 2 so as to allow the demonstration that IL 2 also induced the proliferation of the transferred LAK cells. A variety of studies confirmed that the injected LAK cells were actively proliferating in tissues in vivo under the influence of IL 2. Substitution of "normal" LAK cells with fresh and cultured (without IL 2) splenocytes, or irradiated LAK cells did not result in increased 125IUdR uptake in tissues. Histologic studies corroborated the findings of the 125IUdR incorporation assays and revealed extensive lymphoid proliferation in irradiated mice receiving LAK cells plus IL 2.(ABSTRACT TRUNCATED AT 400 WORDS)     

The anti-tumor efficacy of lymphokine-activated killer cells and recombinant interleukin 2 in vivo: direct correlation between reduction of established metastases and cytolytic activity of lymphokine-activated killer cells

Our previous studies demonstrated that the incubation of human peripheral blood lymphocytes or murine splenocytes in recombinant interleukin 2 (RIL 2) resulted in the generation of lymphokine-activated killer (LAK) cells capable of lysing a broad spectrum of fresh tumors in short-term chromium-release assays. Moreover, injections of LAK cells plus RIL 2 were highly effective in eliminating established 3 day metastases in the lung and liver (1-3). We have examined several parameters to define whether or not the cytolytic activity of LAK cells as measured in vitro correlated directly with the in vivo anti-tumor efficacy of adoptively transferred LAK cells. LAK cells plus RIL 2 could mediate marked reductions of established pulmonary metastases in mice rendered T cell deficient by adult thymectomy and lethal, total body irradiation followed by reconstitution with T cell-depleted bone marrow and spleen cells. Thus there was no requirement for additional T lymphocytes of host origin for successful therapy with adoptively transferred LAK cells plus RIL 2. Fresh splenocytes depleted of T cells by anti-Thy-1.2 monoclonal antibody plus complement generated LAK cells that were as highly lytic to fresh tumor in vitro and were as effective in reducing established pulmonary metastases as those generated from untreated or complement-treated splenocytes. Thus the precursor to LAK cells with anti-tumor activity in vitro and in vivo did not express the Thy-1 antigenic marker. In contrast, treatment of LAK effector cells (those generated from a 3-day incubation of fresh, normal splenocytes in RIL 2) with anti-Thy-1.2 antibody plus complement reduced or abolished their in vitro cytolytic activity. However, when combined with the systemic administration of RIL 2, these T cell-depleted, non-lytic LAK cells remained as effective in reducing the number of established pulmonary metastases upon adoptive transfer as untreated or complement-treated lytic LAK cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

The in vivo distribution of murine lymphokine activated killer cells in splenectomized host

The in vivo distribution of intravenously injected lymphokine activated killer (LAK) cells, generated in vitro with rIL-2 from normal murine splenocytes, was studied in BALB/c mice and compared with that of normal splenocytes. Both normal splenocytes and LAK cells were labeled with 51Cr, and the results were analyzed at 6, 24, and 48 hours after injection by localization index as the parameter. After injection through tail veins of mice, LAK cells were found to migrate to the spleen, lungs, liver, lymph nodes, bones and the kidneys. The apparent increased distribution pattern of LAK cells to the lung at 6 and 24 hours after injection was not detected when normal splenocytes were injected. Since almost one third of the injected LAK cells were found to localize in the spleen, it was postulated that splenectomy would affect the in vivo organ distribution of LAK cells. Accordingly, the in vivo distribution of LAK cells in splenectomized mice was further investigated. Results indicated that splenectomy enhanced the convergence of LAK cells to the lungs, liver, lymph nodes and bones. Therefore, splenectomy may augment the therapeutic effect of the adoptive transfer of LAK cells in pulmonary, hepatic, lymph node and bony metastases.     

Murine lymphokine-activated killer (LAK) cells: phenotypic characterization of the precursor and effector cells

Murine and human lymphocytes incubated in recombinant interleukin 2 (RIL 2) generate a population of cytotoxic cells (lymphokine-activated killer cells [LAK]), which are able to lyse a wide array of fresh tumor cells but do not lyse fresh normal cells. Intravenous administration of these cells with the concomitant administration of RIL 2 can eliminate established pulmonary and hepatic metastases in mice. To characterize the cell that has in vitro LAK activity, we subdivided murine lymphocytes by lysing select subpopulations with the use of complement and antibodies against lymphocyte surface markers or by fluorescence-activated cell sorting. Thy-1.2-negative splenocytes were found to generate near normal amounts of LAK activity after RIL 2 incubation. Small and inconsistent LAK cell activity was generated from Thy-1.2-positive splenocytes. Ia-positive and surface immunoglobulin-positive splenocytes had little or no LAK precursor capability and did not appear to be necessary for LAK activation. Treatment of splenocytes with anti-asialo GM1 (anti-ASGM1) heterosera and complement markedly decreased their ability to generate LAK activity. At the effector stage, cytotoxic cells were of the Thy-1.2-positive, Ia-negative phenotype. Ia-depleted cells were separated into subpopulations bearing or not bearing the gamma Fc receptor (gamma FcR). The majority of cytotoxicity resided in gamma FcR-positive cells. Thus the precursors of murine LAK cells are "null" lymphocytes bearing neither T nor B cell surface markers but develop the Thy-1.2 cell surface marker in vitro, in association with the development of lytic activity for fresh tumor cells after stimulation by RIL 2.     

Immunotherapy of intraperitoneal cancer with interleukin 2 and lymphokine-activated killer cells reduces tumor load and prolongs survival in murine models

The control of malignancy disseminated within the peritoneal cavity is an important problem in the management of low-grade gastrointestinal and ovarian neoplasms. A model of peritoneal carcinomatosis in the mouse was used to investigate the potential of lymphokine-activated killer (LAK) cells and exogenous interleukin 2 (IL-2) to control intraperitoneal tumor. LAK cells are splenocytes activated in vitro by IL-2. C57BL/6 mice were injected intraperitoneally with a lethal inoculum of syngeneic MCA-105 tumor. Three days later, the established tumor was treated with adoptively transferred LAK cells and/or exogenous IL-2 administration. LAK cells alone were ineffective in reducing intraperitoneal tumor. Administration of IL-2 alone resulted in limited tumor reduction. Treatment with exogenous IL-2 in conjunction with LAK cells resulted in the greatest reduction of intraperitoneal tumor. The larger the number of LAK cells given, the greater the reduction in tumor. Frequent intraperitoneal bolus administration of IL-2 was more effective than a single daily intraperitoneal injection and intraperitoneal administration of IL-2 and LAK was more effective than systemic treatments. Marked prolongation of life was seen in mice treated with LAK cells plus exogenous IL-2. We conclude that intraperitoneal LAK cells plus exogenous IL-2 is an effective treatment regimen for reducing intraperitoneal tumor in this murine model.     

Characterization of CD8+ cytotoxic T lymphocyte/tumor cell interactions reflecting recognition of an endogenously expressed murine wild-type p53 determinant

p53 mutations are frequently found in human cancers and are often associated with the overexpression of wild-type (WT) protein or peptide sequences, supporting the notion that WT p53 epitopes may serve as potential targets for tumor immunotherapy. We have developed a cytotoxic T lymphocyte (CTL)/p53 tumor-associated antigen (TAA) model, based on immune recognition of a WT p53 determinant. WT p53-peptide-specific, major histocompatibility complex (MHC) classI-restricted CTL were produced from immunocompetent C57BL/6 (H-2b) mice after immunization with a previously defined WT p53 peptide (p53(232-240)) Epitope-specific CTL were then employed to identify syngeneic tumor cell populations expressing that antigenic determinant. Two syngeneic tumor cell lines, MC38 colon carcinoma and MC57G fibrosarcoma, were demonstrated to express the endogenous WT p53(232-240) determinant naturally, as defined by CD8 + CTL recognition. Cold-target inhibition assays confirmed that CTL-mediated lysis was due to immune recognition of the p53(232-240) peptide epitope. The p53(232-240)-specific CTL line did not lyse syngeneic normal cells (i.e., mitogen-activated splenocytes) in the absence of exogenous peptide, suggesting that the WT-p53-specific CTL could distinguish between tumor cells expressing self-TAA and normal host cells. We have demonstrated, for the first time, that the adoptive transfer of WT-p53-specific CTL to mice with established pulmonary metastasis resulted in antitumor activity in vivo. The ability to generate MHC-class-I-restricted CD8- CTL lines specific for a non-mutated p53 determinant from normal, immunocompetent mice, which display antitumor activity both in vitro and in vivo (by adoptive transfer), may have implications for the immunotherapy of certain p53-expressing malignancies.     

In vivo generation of lymphokine-activated killer cells by sensitization with interleukin 2-producing syngeneic T-lymphoma cells

Culture of C57BL/6 mouse spleen cells with syngeneic EL4 lymphoma cells resulted in no induction of killer cells reactive against EL4 cells. However, in vitro sensitization of C57BL/6 mouse spleen cells with interleukin 2 (IL-2)-producing EL4 lymphoma cells caused the generation of lymphokine-activated killer (LAK) cells, which lyse a variety of tumor cells. Consistent with an in vitro system, we demonstrate that Thy 1.2+, Ly2+, asialo GM1+ LAK cells were successfully induced by in vivo immunization with syngeneic IL-2-producing EL4 lymphoma cells.     

The role of class II MHC molecules in the activation of class I-reactive T cell hybridomas

To examine the role of Ia molecules in T cell responses to allo-class I major histocompatibility antigens, a series of allo-class I-reactive T cell hybridomas was established. Of 134 T cell hybridomas obtained from the fusion of C3H/HeJm or B10.HTT T cells stimulated with C57BL/6 splenocytes, nine T cell hybridomas were reactive to class I antigens and 126 T cell hybridomas were reactive to class II antigens. Six of the nine IL 2-producing T cell hybridomas were further analyzed: five mapped to H-2Kb and the other mapped to H-2Db. Three of these T cell hybridomas, HTB-157.7, HTB-176.10, and HTB-177.2, could react to the EL-4 cell line that expresses H-2Kb and H-2Db class I antigens but lacks class II I-Ab molecules. Furthermore, the activation of these three T cell hybridomas with C57BL/6-derived splenocytes was not blocked by either anti-I-A or anti-L3T4 antibody. In contrast, the other three T cell hybridomas, CB-127.6, CB-221.7, and HTB-102.7, failed to react with EL-4 but reacted with the LB cell line which expresses class I (H-2Kb, H-2Db) and class II (I-Ab) molecules. Although class II molecules were required for activation of the latter clones, there was no apparent I-A allele specificity, suggesting that a relatively nonpolymorphic Ia determinant was involved. The activation of the three latter T cell hybridoma clones with C57BL/6 splenocytes could be blocked completely by either anti-I-A or anti-L3T4 antibody. The data are interpreted in terms of possible T cell receptor models for recognition of class I with nonpolymorphic class II determinants.     

H-2 antigen expression: Loss in vitro,restoration in vivo,and correlation with cell-mediated cytotoxicity in a mouse lymphoma cell line

The susceptibility to cell-mediated cytolysis of cells of the recently developed C57BL/Ka(H-2 ^b ) lymphoma cell line, BL/VL₃, was investigated in allogeneic assays with thymus-dependent lymphocytes (T cells). Compared to EL4, the widely used C57BL/6(H-2 ^b ) lymphoma cell line, BL/VL₃ cells were found to be insensitive to T-cell-mediated lysis as detected by the use of⁵¹Crrelease methods. When used as immunogens in alloreactive combinations with BALB/c(H-2 ^d ) splenocytes as responder cells, BL/VL₃ cells failed to elicit sensitization. Serological tests showed that this cell line had profoundly reduced levels of H-2^b antigens on its surface. When BL/VL₃ cells were reinjected into C57BL/Ka and BALB/c mice, full recovery of H-2^b antigen expression at the cell surface was observed in both syngeneic and allogeneic hosts after only 11 days of in vivo growth. Concomitantly, they acquired the ability to induce cytotoxic responses in allogeneic T cells and became susceptible to their lytic activity. The expression of H-2 antigens on the surface of BL/VL₃ cells is a reversibly modulated function that depends on in vivo growth conditions and is lost in vitro in the absence of immunoselective pressure.     

Inverse relationship in H-2-associated lysis between NK cells and rIL-2-activated killer cells: evidence from in vitro killing and metastatic experiments

We investigated the manner in which rIL-2 induced effectors in vitro (LAK cells), which, like NK cells, lyse targets nonspecifically and discriminate nonself, and how H-2 as the self-marker affects the LAK cell killing mechanism. NK cells showed an appreciably higher killing activity to B16 melanoma H-2- cells than to H-2+ cells. In contrast, LAK cells lysed more efficiently to H-2+ cells. The in vivo experiments showed that the NK cells prevented pulmonary metastasis of B16 H-2- cells in the normal syngeneic host, whereas the transferred LAK cells had a preferential inhibitory effect on the pulmonary metastasis of B16 H-2+ cells in the immunodeficient syngeneic hosts. Taken together, these results show that the H-2-encoded or H-2-associated molecules contribute to the triggering signal in the lysis by LAK cells, whereas the NK cells recognize the reduced self H-2 expression on the targets, thereby contributing to a trigger of the lysis.     

Evidence that lymphokine-activated killer cells and natural killer cells are distinct based on an analysis of congenitally immunodeficient mice

The in vitro incubation of lymphoid cells in RIL 2 results in the generation of LAK cells that are broadly lytic to autologous, syngeneic, and allogeneic fresh tumor cells, but which do not lyse fresh, normal cells. Strains of mice with congenital immunodeficiencies were tested both for the presence of NK cells and for their capacity to generate LAK cells after in vitro incubation with IL 2. Splenocytes obtained from two immunodeficient mouse strains (NIH-Beige-Nude and NIH-Beige-Nude-XID) failed to generate LAK cells, but displayed significant activity. Splenocytes from another immunodeficient mouse strain (NIH-Beige-XID) generated LAK cells but did not display NK cell activity. This dissociation of activation of LAK cells from NK cells among the immunodeficient strains indicates that the LAK and NK cell lytic systems are distinct.     

Adoptive transfer of H-2-incompatible lymphokine-activated killer (LAK) cells: an approach for successful cancer immunotherapy free from graft-versus-host disease (GVHD) using murine models

We investigated whether the adoptive transfer of H-2-incompatible lymphokine-activated killer (LAK) cells would efficiently demonstrate antitumor activity without damaging the normal host cells. Allogeneic LAK cells (5 X 10(7] did not cause graft-versus-host disease (GVHD) in irradiated recipients, whereas more than half of the mice transferred with the same dose of fresh allogeneic spleen cells developed GVHD. Repeated transfer (three times at 4-day intervals, 1.2 X 10(8) cells/mouse) did not result in GVHD. Graft-versus-host reaction (GVHR), which is detectable by spleen enlargement of recipients transferred with allogeneic lymphoid cells was also absent in LAK cell-transferred mice of all strain combinations tested. Host immune responses were not affected in these mice. Therefore, it is feasible to transfer allogeneic LAK cells. With the antitumor efficacy of allogeneic LAK cells, they preferentially lysed allogeneic tumor targets. Adoptive transfer of the allogeneic LAK cells led to a significant decrease in the lung-colonizing foci of intravenously inoculated B16 melanoma cells. Allogeneic LAK cells and syngeneic ones were equally active, in vivo. The use of allogeneic LAK cells may prove to be a valuable method for effective clinical antitumor immunotherapy.     

Characterization of IL-2-induced murine cells which exhibit ADCC activity

The incubation of murine splenocytes in recombinant interleukin 2 (IL-2) gives rise to both lymphokine-activated killer (LAK) cells capable of lysing fresh tumor cells and cells capable of mediating antibody-dependent cellular cytotoxicity (ADCC) in the presence of anti-H2 allosera. A similarity between these two IL-2-induced cell populations was found. The precursors of the cells mediating these activities were shown to be ASGM1 positive, Thy 1 negative, and radiosensitive. Cells taken from the spleen, thymus, and bone marrow were able to mediate ADCC after culture in IL-2. The effector cell was either Thy 1 positive or negative and was less affected by anti-Thy 1 plus C' treatment than cells which mediated LAK activity. In addition ADCC was exhibited in IL-2-cultured splenocytes from various murine strains and correlated with their LAK activity with one exception. While IL-2-cultured C57BL/6 splenocytes exhibited LAK activity similar to that of C3H LAK cells, no ADCC activity could be demonstrated in C57BL/6 cells. Study of the difference in the ability of these two strains to mediate ADCC revealed that IL-2-induced FcR+ cells in C3H thymocytes, but not in C57BL/6 thymocytes. Based on FACS analysis and on the radiosensitivity of the induction of both FcR+ cells and ADCC, it was suggested that IL-2 was expanding a small FcR+ cell population rather than inducing an increase in FcR density on the cell surface. The relationship between the IL-2-induced ADCC mediator and other IL-2-induced cells, as well as ADCC effector cells, and the possible implications of the results for the in vivo therapy of cancer based on ADCC are discussed.     

Mycophenolate mofetil does not suppress the graft-versus-leukemia effect or the activity of lymphokine-activated killer (LAK) cells in a murine model

Background: Graft-versus-leukemia (GVL) effect is an essential component in the course of allogeneic stem cell transplantation (SCT). However, both prevention and treatment of established graft-versus-host disease (GVHD), including with drugs such as cyclosporine, can suppress GVL effects. Mycophenolate mofetil (MMF) is becoming a standard of care in SCT recipients for better prevention of GVHD as well as for promoting stem cell engraftment. Aims: To evaluate the effect of MMF, an immunosuppressive drug increasingly used for prevention of GVHD, on disease recurrence following SCT in a preclinical animal model. Since GVL effects may be also induced by alloreactive natural killer (NK) cells, the goal was to investigate the effects of MMF on the activity of lymphokine-activated killer (LAK) cells. Methods: MMF was administered by daily intraperitoneal injection starting at day 1 post-SCT. Cytotoxic LAK activity was measured by 5-h ³⁵S-release assay, and GVL was tested by the appearance of BCL1 leukemia in a semi-mismatched (C57BL/6 donors to [BALB/c × C57BL/6] F₁ recipients) murine model. Results: A dosage regimen of 28–200 mg/kg per day MMF had no negative effect on either cytotoxic LAK activity or GVL (as measured by finding of leukemic cells in recipient spleen by PCR or the appearance of clinical leukemia with adoptive transfer). Conclusions: These results suggest that MMF does not impair GVL effects or reduce LAK cell activity in mice.     

In vivo migration and tissue localization of highly purified lymphokine-activated killer cells (A-LAK cells) in tumor-bearing rats

Our laboratory has previously reported that the adoptive transfer of highly purified lymphokine-activated killer cells (adherent-LAK, A-LAK) into Fischer 344 (F344) rats bearing established lung or liver micrometastases effectively reduced the resultant tumor growth more than 90%, leading to significant increases in animal survival (Cancer Res. 49, 1441, 1989). To begin to investigate the mechanism(s) by which A-LAK cells mediate this anti-tumor effect, we studied their migration patterns in F344 rats bearing experimentally induced lung and liver metastases as well as subcutaneous tumors. A-LAK cells which were phenotypically 95 to 100% natural killer cells/large granular lymphocytes were labeled with either 51Chromium or fluorescein diacetate (so as to be visualized microscopically). Intravenous injection of such labeled A-LAK cells did not show significant differences in their tissue distribution patterns in tumor-bearing versus normal rats, even when high levels of exogenous recombinant interleukin-2 (rIL-2) was administered. A-LAK cells first migrated to the lungs and then subsequently migrated to the liver and spleen as early as 2 to 6 hr following iv injection. The kinetics of exit of A-LAK cells from the pulmonary capillary beds was not significantly different in rats bearing 3-day micrometastases or 14-day macrometastases compared to normal rats. Moreover, the presence of metastases in the liver did not alter the extent or kinetics of entry of A-LAK cells into the liver even in the presence of exogenously administered rIL-2. Finally, in rats bearing subcutaneous tumors, no evidence could be obtained that A-LAK cells were selectively localized to the tumor site. Tissue sections of livers from metastases-bearing animals injected with fluorescein diacetate labeled A-LAK cells did not demonstrate significant numbers of A-LAK cells infiltrating tumor nests with or without the administration of exogenous IL-2. These data suggest that A-LAK cells may mediate tumor regression in vivo by direct and indirect mechanisms, possibly through the secretion of cytokines and/or the recruitment of secondary effector cells.     

Antigen-dependent proliferation of cloned continuous lines of H-2-restricted influenza virus-specific cytotoxic T lymphocytes

The antigenic requirements for in vitro proliferation of several cloned continuous lines of H-2-restricted influenza virus-specific cytotoxic T lymphocytes (CTL) has been examined. The cloned CTL lines were established from individual splenic CTL precursors obtained from A/JAPAN/305/57 (H2N2)-immune F1 (C57BL/6 X BALB/c) donors. The lines were isolated (by limiting dilution in liquid culture) and expanded in the presence of A/JAPAN/305/57-infected irradiated syngeneic (F1) spleen cells and T cell growth factor (TCGF) of rat spleen origin. Optimal proliferation (and long-term in vitro cultivation) of these H-2-restricted CTL lines required both specific antigenic stimulation in the form of virus-infected syngeneic spleen cells and an exogenous source of TCGF. In addition, the antigenic requirements for proliferation of these lines directly reflected the pattern of H-2-restricted influenza virus-specific recognition at the level of target cell recognition and lysis.     

Influence of T cells on the expression of lymphokine-activated killer cell activity and in vivo tissue distribution

Lymphokine-activated killer (LAK) cells are currently being evaluated in several cancer centers for the immunotherapy of patients with a variety of cancers. Understanding the in vivo distribution of LAK cells should help to optimize their antitumor efficacy. As a model system to examine this issue, nylon wool column-passed rat lymphocytes were cultured in the presence of rIL-2 for 1 and 2 days. The resulting cells were divided into two populations; one that adhered to the plastic flasks and the second which did not adhere. The adherent cells were found to be highly cytotoxic against NK-sensitive and NK-resistant targets, whereas the nonadherent cells were unable to kill NK-resistant targets unless T cells were removed from this population. These results indicate that T cells present in IL-2 activated bulk splenocytes may interfere with the activity of LAK cells. Adherent or nonadherent LAK cells were evaluated for their pattern of in vivo distribution after i.v. inoculation. These cells were found to display a restricted pattern of distribution, localizing mainly in the lungs at 2 h after i.v. injection but redistributing into the liver and the spleen by 24 h. LAK cells were rarely recovered from the lymphoid tissues, including the peripheral lymph nodes and the mesenteric lymph nodes. However, if T cells were not removed from the LAK cell population, some radioactivity was recovered from the peripheral and mesenteric lymph nodes. Fractionation of 2 day-activated, nonadherent population on discontinuous Percoll resulted in the enrichment of large granular lymphocyte (LGL)/LAK activity in low density fractions (42% and 45% Percoll), whereas high density fraction (70% Percoll) contained T cells which showed no cytolytic activity. Upon transfer into syngeneic rats, the 42% fraction showed typical LAK migration. In contrast, the 70% fraction showed typical T cell migration. What is more important, removal of the granulated cells resulted in a population which have no granules and resemble large agranular lymphocytes known to be pre-LGL/LAK cells. Large agranular lymphocytes showed a pattern of distribution different from both T and LGL/LAK cells.