Induction of graft versus leukemia effects by cell-mediated lymphokine-activated immunotherapy after syngeneic bone marrow transplantation in murine B cell leukemia

 The feasibility of inducing graft versus leukemia (GVL) effects with allogeneic T cells in recipients of autologous bone marrow transplantation (BMT) was studied in a murine model (BCL 1) of human B cell leukemia/lymphoma. Allogeneic cell therapy, induced by infusion with peripheral blood lymphocytes, a mixture of allogeneic spleen and lymph node cells and allogeneic activated cell therapy, induced by in vitro recombinant-interleukin-2(rIL-2)-activated allogeneic bone marrow cells in tumor-bearing mice, prevented disease development in adoptive BALB/c recipients. Concomitant in vivo activation of allogeneic lymphocytes with rIL-2 suppressed even more effectively the development of leukemia in secondary adoptive recipients of spleen cells obtained from treated mice. In contrast, in vivo administration of rIL-2 after syngeneic BMT, with or without equal numbers of syngeneic lymphocytes, led to disease development in secondary recipients. Our data suggest that effective cell therapy can be achieved after SBMT by allogeneic but not syngeneic lymphocytes and that anti-leukemic effects induced by allogeneic lymphocytes can be further enhanced by in vitro or in vivo activation of allogeneic effector cells with rIL-2. Therefore, cell therapy by allogeneic lymphocytes following autologous BMT could become an effective method for inducing GVL-like effects on minimal residual disease provided that graft versus host disease can be prevented or adequately controlled. Received: 14 May 1996 / Accepted: 6 August 1996     

Activation of nonspecific killer cells by interleukin 2-containing supernatants

In the absence of specific antigen stimulation, nonspecific killer cells were induced by culturing C57BL/6 lymph node or spleen cells with interleukin 2-containing supernatants. These supernatants were obtained from stimulation of either rat spleen cells with concanavalin A or a variant of the T cell lymphoma, EL4 (H-2b) with phorbol myristic acetate. The ability of the EL4 supernatant to induce nonspecific killer cells was abrogated by absorption with an interleukin 2-dependent T cell line or by concanavalin A-stimulated spleen cell blasts, but not by lipopolysaccharide-stimulated spleen cell blasts or by a non-interleukin 2-producing EL4 line. Partially purified interleukin 2 from EL4 supernatants could also support nonspecific killer cell induction. The induction of cytolytic cells by interleukin 2 is sensitive to gamma-irradiation and has a D omicron of 120 rad. The nonspecific killer cells induced are likely cytotoxic T lymphocytes; the majority of the precursor and effector cells bear the Thy-1 alloantigen marker. These nonspecific killer cells killed a broad spectrum of target cells, including concanavalin A- and lipopolysaccharide-induced splenic blasts of syngeneic or allogeneic mice, a syngeneic tumor, and a cloned allogeneic cytotoxic T cell line. The frequency of precursors for nonspecific killer cells in C57BL/6 lymph node and spleen cells are 1/7000 and 1/12,000, respectively. Clonal analyses revealed that these nonspecific killers exhibit heterogeneity with respect to their target cell specificities. The induction of nonspecific killers by interleukin 2-containing supernatants is partially dependent on nylon wool-adherent cells; in antigen-stimulated cultures the most specific killer cells were obtained from cultures in which nylon wool-nonadherent lymph node responder cells were stimulated with nylon wool-nonadherent allogeneic splenic stimulator cells that were treated with anti-Thy-1 antibody and complement. The relevance of these findings with respect to the frequencies and fine specificities of cytotoxic T lymphocytes generated in interleukin 2-supplemented cultures is discussed.     

Characterization of Effector Cells against B16 Melanoma in Mice Inoculated with Allogeneic Spleen Cells

Inbred C57BL/6 (B6) mice which had received an inoculation of allogeneic spleen cells showed remarkable antitumor activity against syngeneic tumor challenge with B16 melanoma cells 3 days after the allogeneic cell inoculation. This antitumor activity was not specific to the inoculated alloantigen, since the challenging B16 cells are syngeneic to B6 mice and since it was induced by BALB/c spleen cells as well as C3H/He spleen cells. The antitumor activity was sensitive to an in vivo treatment with anti-asialo GM1 (AGM1) antiserum or anti-Thy.1 monoclonal antibody (mAb) just before the tumor challenge and was resistant to an in vivo treatment with anti-CD8 (Ly. 2) mAb. These results suggest that AGM1+Thy.1+CD8– activated natural killer (NK) cells were generated by alloantigen inoculation and took an important part in the antitumor effect of the alloantigen inoculation.     

Superior anti-tumor protection and therapeutic efficacy of vaccination with allogeneic and semiallogeneic dendritic cell/tumor cell fusion hybrids for murine colon adenocarcinoma

Cancer immunotherapy by dendritic cell (DC)/tumor cell fusion hybrids (DC/TC hybrids) has been shown to elicit potent anti-tumor effects via the induction of immune responses against multiple tumor-associated antigens. In the present study, we compared the anti-tumor effects of vaccinating Balb/c mice (H-2^d) with CT26CL25 colon carcinoma cells that had been fused with either syngeneic DCs from Balb/c mice, allogeneic DCs from C57BL/6 mice (H-2^b) or semiallogeneic DCs from B6D2F1 mice (H-2^b/d). Preimmunization with either semiallogeneic or allogeneic DC/TC hybrids induced complete protection from tumor challenge, whereas mice preimmunized with syngeneic DC/TC hybrids were only partially protected (75% tumor rejection). The average number of pulmonary metastases after intravenous tumor injection decreased significantly following immunization with semiallogeneic or allogeneic DC/TC hybrids (8.3 ± 7.9 or 16.3 ± 3.5, mean ± SD) relative to syngeneic DC/TC hybrids (67.8 ± 6.3). These data demonstrate that vaccination with semiallogeneic DC/TC hybrids resulted in the greatest anti-tumor efficacy. Anti-tumor effects showed by in vivo studies were virtually accomplished by the frequency of induced CTLs specific to both gp70 and β-galactosidase assessed by using pentameric assay. Among the fusion vaccines tested, semiallogeneic DC/TC hybrids induced the highest ratio of Th1 cytokine IFN-γ to Th2 cytokine IL-10. In addition, allogeneic or semiallogeneic DC/TC hybrids elicited a significantly stronger NK activity than syngeneic DC/TC hybrids. These findings suggest that in clinical settings, DCs derived from a healthy donor (which are generally characterized as more semiallogeneic than allogeneic) may be more capable than autologous DCs of inducing promising anti-tumor effects in vaccinations with DC/TC hybrids.     

Studies of the immunological capacity of germfree mouse radiation chimeras. III. In vitro reconstitution of the T-helper cell deficiency

The plaque-forming cell (PFC) response of long-term radiation induced allogeneic bone marrow chimeric (ABMC) mice has been shown to be markedly deficient. The nature of the cellular deficiency of the primary PFC response was investigated using in vitro culture techniques. Adherent spleen cells from ABMC or DBA/2 mice support equally well the development of PFC from nonadherent DBA/2 spleen cells. Nonadherent cells prepared from ABMC mice when cocultivated with DBA/2 adherent cells showed a minimal response. However, the addition of activated DBA/2 T cells to cultures containing adherent cells from DBA/2 mice and nonadherent cells from ABMC mice completely reconstituted the in vitro response to sheep erythrocytes. Therefore a cellular deficiency of the humoral immune system of ABMC mice was shown to be associated with the thymus-derived lymphocyte pool.     

Cell-Cooperation in Anti-Sheep Red Blood Cell Antibody Response in Mouse Spleen Cell Cultures

Restoration of impaired antibody response to sheep red blood cells (SRBC) in spleen cell cultures from mice treated with heterologous antilymphocyte globulin (ALG) was studied by adding normal cells from various sources, to explore the problems of cell-cooperation in anti-SRBC antibody response and the target of ALG. When spleen cells from ALG-treated mice were separated into macrophage-rich and lymphoid cell-rich subpopulations, only the latter was found to be impaired in the ability for anti-SRBC antibody response. Addition of even a small number of normal allogeneic spleen cells sufficiently restored the impaired anti-SRBC antibody response of the spleen cells from ALG-treated mice. By use of allo-antisera, most hemolysin plaque-forming cells (PFC) generated in such cultures were proved to be derived from the cells of ALG-treated mice. Restoration was also achieved by adding thymus-derived cells, which were obtained from spleens of mice heavily irradiated and repopulated with syngeneic thymus cells, or lymphoid cells directly collected from thymuses. All results indicate that ALG selectively depletes the thymus-derived antigen reactive cells (ARC) in the spleen cell population, and that ARC supplied from normal spleen or thymus can interact with plaque-forming cell precursors (PFCP) that remain intact in the spleen cell population of ALG-treated mice. The results also suggest that a single ARC interacts with more than one PFCP and makes them develop into PFC.     

Secondary in vitro generation of CTL specific for MM antigen by stimulation with somatic tumor hybrid, but not with parental tumor cells

Somatic tumor hybrid cells (L-FM3A#2), obtained by hybridization of MM tumor cells (FM3A/R) with HGPRT-less L cells, could induce CTL directed against MM antigen, a tumor-associated transplantation antigen that is expressed on some ascitic mammary tumor cell lines of C3H/He mice; parental tumor cells (FM3A/R) could not produce such CTL in syngeneic mice. In this study, the mechanisms of the generation of CTL by stimulation with L-FM3A#2 hybrid cells were investigated. In the secondary in vitro stimulation system, L cell component(s) that were introduced into hybrid cells by cell fusion play a role in the induction of CTL, as shown by the fact that stimulation with a mixture of L and FM3A/R cells could induce MM antigen-specific CTL, and that the killer helper effect of L cells could be replaced by cell free culture supernatants obtained from co-cultures of unprimed C3H spleen and L cells. IFN activity, but no IL 2 activity, was detected in the culture supernatants. Both IFN and killer helper activity were lost with pH 2 treatment; furthermore, CTL were generated by stimulation of primed spleen cells with FM3A/R cells in the presence of mouse beta-IFN, but not in its absence. These results suggest that IFN liberated by the helper cells that recognize L cell component(s) on the surfaces of tumor hybrid cells plays an essential role in the generation of CTL specific for MM antigen.     

Composition of the immune system of allophenic mice.

Mice were immunized with antigen (Rabbit Fab' fragments) attached to syngeneic, or f₁ (semi-syngeneic) irradiated spleen cells. Specific anti-rabbit Fab' plaque forming cell numbers showed that the response towards antigen on syngeneic or F₁ cells, was significantly lower than that towards the same antigen on allogeneic cells. By subsequent in vitro incubation of immune spleen cells with antigen followed by plaque assay, it was found that those spleen cells exhibiting lowered plaque forming cell numbers initially, (i.e., those mice immunized with antigen on syngeneic or F₁ cell surfaces) showed, after incubation, a response equal to or greater than those cells which initially (before in vitro incubation) demonstrated a larger response (i.e. those mice immunized with antigen on allogeneic cells).     

Studies of thymopoietin pentapeptide (TP5) on experimental tumors: I. TP5 relieves immunosuppression in tumor-bearing mice

The allogeneic and syngeneic immune responses of tumor-bearing mice (C57BL/6 mice bearing 3LL and DBA mice bearing P815) were evaluated by the cytotoxic lymphocyte precursor unit (CLP-U) and MLC. In general, tumor-bearing mice showed slightly enhanced immune responses 4 days after tumor inoculation. This enhanced immune response rapidly declined and about 7–10 days after tumor inoculation, both allogeneic and syngeneic responses were markedly lower than normal. Mice treated with TP5, starting 2 weeks before tumor inoculation, retained normal or enhanced allogeneic and syngeneic responses up to 3 weeks after tumor inoculation. When this tumor-induced suppressive effect was studied in cell transfer experiments, spleen cells from tumor-bearing mice enhanced the growth of tumors in syngeneic recipients whereas spleen cells from TP5-treated mice inhibited the growth of tumors in syngeneic recipients. Moreover, the spleen cells from TP5-treated mice also showed enhanced cytotoxic activity against tumor cells in vitro. These findings suggest that the tumors, after a transient stimulatory phase, induced immune suppressive mechanisms in the hosts' immune defenses. Treatment with TP5 prevented the development of these immune suppressive effects and spleen cells from TP5-treated tumor-bearing mice inhibited tumor growth in freshly tumor-inoculated recipients.     

Suppression of natural killer (NK) cell activity of spleen cells by thymocytes

The in vitro influence of thymus cells on natural killer cell activity of spleen cells against prelabeled target cells (YAC-I and RL♂I) has been studied in syngeneic as well as in allogeneic murine models. In mixing experiments to demonstrate suppression, total thymocytes have been found to have no effect on NK activity of syngeneic or allogeneic spleen cells. Among several thymocyte fractions separated by velocity sedimentation, a relatively faster sedimenting fraction showed remarkable suppression of NK activity by spleen cells against two target cells. The suppressive effect of this particular fraction on NK activity was demonstrated to be proportional to the cell dose. The suppressive function was resistant to irradiation at 1000 or 2000 rad administered in vitro and was not restricted by the major histocompatibility complex. Moreover, the thymocyte fraction which induced suppression was not sensitive to NK-mediated cytolysi? by syngeneic spleen cells. The suppression of NK cytolysis in vitro by certain subpopulations of thymocytes as observed in the present studies may be consistent with a role for the thymus in regulating NK activity in vivo.     

Immune dysfunction associated with graft-vs-host reaction in mice transplanted across minor histocompatibility barriers. II. Reversible defect in T-dependent antibody responses

B cell and Th cell functions were assessed in mice undergoing a graft-vs-host reaction (GvHR) in response to minor histocompatibility Ag by using the plaque-forming cell (PFC) response to the T-independent Ag TNP-Brucella abortus and the T-dependent Ag TNP-SRBC. Bone marrow plus spleen cells from B10.D2 mice were transplanted into lethally irradiated B10.D2 (syngeneic recipient) or H-2d-compatible BALB/c (allogeneic recipient) to produce a chronic form of GvHR. BALB/c recipients of an allogeneic transplant demonstrated a marked and proportional lymphoid depletion of the spleen with normal percentages of B cells, T cells, and CD4+ and CD8+ T cell subsets. Mice with GvHR made normal numbers of PFC/10(5) spleen cells in response to the T-independent Ag, but a significantly depressed number of PFC/10(5) spleen cells to the T-dependent Ag compared with normal B10.D2 mice and with irradiated B10.D2 recipients of syngeneic B10.D2 marrow plus spleen cells. Mice undergoing the minor Ag GvHR made significantly larger numbers of PFC/10(5) spleen cells after secondary immunization with TNP-SRBC compared with controls. In vitro assays demonstrated that B cells from mice with GvHR responded to T help from normal B10.D2 mice and that T cells from mice with GvHR provided help to normal B cells after in vivo immunization. These data demonstrate that radiation chimeras with GvHR in response to minor histocompatibility Ag have relatively normal B cell function and an apparent defect in T helper cell function that is reversible by immunization with appropriate Ag.     

Properties of syngeneic and allogeneic antisera raised to tumor-specific suppressor factor from DBA/2J mice

Summary Tumor-specific suppressor factor was prepared by injecting soluble membrane extracts of the syngeneic mastocytoma, P815, into DBA/2J mice 4 days prior to sacrifice. The suppressor factor was purified by passage of spleen extracts over an immunoadsorbent containing P815 membrane components. Antisera raised in syngeneic and allogeneic (C57Bl/6) mice by repeated injections of suppressor factor were tested. It was found that these antisera, but not their controls, were capable of absorbing out the suppressor factor. The antisera were also capable, in the presence of complement, of eliminating suppressor cells from suppressive spleen cell populations. However, the antisera were not capable of eliminating syngeneic tumor-specific in vitro-generated killer cells, indicating that the receptor molecules on suppressor and effector cells in this system are distinct from each other.     

In vitro induction of polyclonal killer T cells with 2-mercaptoethanol and the essential role of macrophages in this process.

Killer T cells against allogeneic and syngeneic tumor cells were generated in vitro by the addition of 2-mercaptoethanol (2-ME) to the murine spleen cell culture in the absence of any antigenic stimulation. The maximum activity of T cell-mediated cytotoxicity (CMC) induced with 2-ME was observed on day 4 of culture and the induction of CMC was completely inhibited by the addition of inhibitor of DNA synthesis, hydroxyurea, or cytosin arabinoside. CMC induced with 2-ME was specifically inhibited by the addition of unlabeled target cells to the 51Cr-release assay system. These results indicated that killer T cells were generated in the presence of 2-ME as a result of nonspecific polyclonal activation of precursors into cytotoxic effector cells and that they recognized target cells with antigen-specific recognition receptors. Spleen cells deprived of adherent cells showed impaired induction of CMC with 2-ME. The addition of peritoneal exudate macrophages to splenic T cells restored this response. The result indicated that macrophages were essential for the induction of CMC with 2-ME. The possibility that the function of macrophages was mediated by soluble factor(s) released from macrophages was demonstrated by the separate culture of splenic T cells and macrophages in double-chambered, Marbrook-type vessels and by the addition of supernatants from macrophage cultures to splenic T cells. 2-ME and soluble factor(s) released from macrophages seemed to be required for the activation of precursors into killer cells.     

T-T cell interaction in the induction of delayed-type hypersensitivity (DTH) responses: vaccinia virus-reactive helper T cell activity involved in enhanced in vivo induction of DTH responses and its application to augmentation of tumor-specific DTH responses

The role of antigen-specific helper T cells in augmenting the in vivo development of delayed-type hypersensitivity (DTH) responses was investigated. C3H/HeN mice were inoculated i.p. with vaccinia virus to generate virus-reactive helper T cell activity. These vaccinia virus-primed or unprimed mice were subsequently immunized subcutaneously (s.c.) with either trinitrophenyl (TNP)-modified syngeneic spleen cells (TNP-self), vaccinia virus-infected spleen cells (virus-self), or cells modified with TNP subsequent to virus infection (virus-self-TNP). Seven days later, these mice were tested for anti-TNP DTH responses either by challenging them directly with TNP-self into footpads or by utilizing a local adoptive transfer system. The results demonstrated that vaccinia virus-primed mice failed to generate significant anti-TNP DTH responses when s.c. immunization was provided by either virus-self or TNP-self alone. In contrast, vaccinia virus-primed mice, but not unprimed mice, could generate augmented anti-TNP DTH responses when immunized with virus-self-TNP. Anti-vaccinia virus-reactive helper activity was successfully transferred into 600 R x-irradiated unprimed syngeneic mice by injecting i.v. spleen cells from virus-primed mice. These helper T cells were found to be antigen specific and were mediated by Thy-1+, Lyt-1+2- cells. DTH effector cells enhanced by helper T cells were also antigen specific and were of the Thy-1+, Lyt-1+2- phenotype. Furthermore, vaccinia virus-reactive helper T cell activity could be applied to augment the induction of tumor-specific DTH responses by immunization with vaccinia virus-infected syngeneic X5563 tumor cells. T-T cell interaction between Lyt-1+ helper T cells and Lyt-1+ DTH effector T cells is discussed in the light of the augmenting mechanism of in vivo anti-tumor-specific immune responses.     

Defective T helper activity in the spleen of BALB/c mice immune to a syngeneic fibrosarcoma

Summary BALB/c mice were immunized with the syngeneic 3-methylcholanthrene-induced fibrosarcoma CA-2 by the growth and excision method. When lymphoid cells from different organs of these tumor-free mice were tested in a direct ⁵¹Cr-release assay, peritoneal exudate cells but not spleen cells displayed specific cytotoxicity against the syngeneic tumor target. A cytotoxic response could be obtained by tumor-immune spleen cells when cultured in a mixed lymphocyte tumor cell culture (MLTC) at high but not low density although at the same effector/stimulator ratio. Lack of cytotoxic activity in low density MLTC was not due to an impairment of cytotoxic precursors since cytotoxicity was rescued by adding exogenous interleukin-2 in experimental conditions in which no lymphokine-activated killer cells could develop relevant anti-CA-2 lysis. When low density MLTC were supplemented with either 800 R-irradiated cells or nonirradiated, negatively selected Lyt 1⁺ cells from the same immune mice, induction of a cytotoxic response against CA-2 occurred and interleukin-2 production became detectable. Additional studies indicated that spleen cells of CA-2-immune mice were also impaired in their ability to provide help to syngeneic thymocytes for the generation of cytotoxic T lymphocytes against C57BL/6J alloantigens. Dilution effect of helper cells due to immunization procedures was excluded since spleen cells of mice immunized against another BALB/c tumor, the YC8 lymphoma, or against DBA/2 minor histocompatibility antigens provided good help to thymocytes against the same alloantigens. These results indicate that tumor-immune animals may also have selective T helper defects in an important lymphoid organ like spleen.     

Generation of T helper cells in vitro. IV. F1 T helper cells primed with antigen-pulsed parental macrophages are genetically restricted in their antigen-specific helper activity.

A sequential culture technique for the in vitro induction and subsequent assay of T helper cells is employed to examine the histocompatibility requirements for antigen recognition by murine T helper cells. F1 T cells are primed in vitro with antigen-pulsed parental strain macrophages and tested for antigen-specific helper activity in cultures containing anti-Thy 1.2 serum and C treated spleen cells from hapten-primed parental or F1 mice. A semiallogenieic system is used and appropriate controls are included to avoid possible complicating effects of allogeneic interactions. The results indicate that F1 T helper cells preferentially stimulate carrier-specific anti-hapten plaque-forming cell responses in spleen cells which are H-2 identical with the macrophage used initially to prime the T cells. Parental spleen cell cultures do not respond to F1 T helper cells which were primed with the other parental strain macrophage. Supplementing this culture with macrophages which are histocompatible with those used to prime the F1T cells is sufficient to restore T helper cell activity. Thus, the genetic restriction described here is between the primed T cell and the macrophage used to elicit secondary responses and not between the T cell and B cell. The results in this semiallogeneic system, however, do not rule out the possibility of additional allogeneic genetic restrictions in the subsequent interaction of T cells with B cells.     

In vivo antitumor effects of murine interferon- γ -inducing factor/interleukin-18 in mice bearing syngeneic Meth A sarcoma malignant ascites

Interferon-γ-inducing factor/interleukin-18 is a novel cytokine that reportedly augments natural killer (NK) activity in human and mouse peripheral blood mononuclear cell cultures in vitro and has recently been designated IL-18. In this study, IL-18 exhibited significant antitumor effects in BALB/c mice challenged intraperitoneally (i.p.) with syngeneic Meth A sarcoma when administered i.p. on days 1, 2 and 3 after challenge. Intravenous (i.v.) administration also induced antitumor effects in the tumor-bearing mice; however, subcutaneous (s.c.) administration did not. When mice were twice pretreated with 1 μg IL-18 3 days and 6 h before tumor challenge, all mice survived whereas control mice died within 3 weeks of challenge. Inhibitory effects on Meth A cell growth in vitro were not observed with either IL-18 or interferon γ. The effects of IL-18 pretreatment were abrogated by abolition of NK activity after mice had been injected with anti-asialo GM1 antibody 48 h before and, 24 h and 72 h after tumor challenge. Mice pretreated with IL-18 and surviving tumor challenge resisted rechallenge with Meth A cells but could not reject Ehrlich ascites carcinoma, and spleen cells from the resistant mice, but not control mice, exhibited cytotoxic activity against Meth A cells in vitro after restimulation with mitomycin C-treated Meth A cells for 5 days. The effector cells in the spleen cell preparations from resistant mice appear to be CD4⁺ cells because cytolytic activity was significantly inhibited after depletion of this subset by monoclonal antibodies and complement. In conclusion, IL-18 exhibits in vivo immunologically (primarily NK) mediated antitumor effects in mice challenged with syngeneic Meth A sarcoma and induces immunological memory and the generation of cytotoxic CD4⁺ cells. Received: 17 September 1996 / Accepted: 8 November 1996     

Induction of activated natural killer cells from murine spleen cells primed in vivo and subsequently challenged in vitro with the streptococcal preparation OK432

Summary The present study shows that natural killer cell-mediated cytotoxicity of BALB/c mouse spleen cells to syngeneic tumor cells was augmented by in vivo priming or in vitro stimulation with the streptococcal preparation OK432. The augmentation of spleen cell cytotoxicity to syngeneic tumor cells by in vivo priming alone with OK432 was lower than that obtained by in vitro stimulation alone with OK432. When the murine spleen cells primed in vivo with OK432 were rechallenged in vitro with OK432 at various intervals, the natural cytotoxicity was more strongly enhanced than that seen with in vitro stimulation alone. The cell surface phenotype of killer cells activated with OK432 was Thy 1⁺ and asialo GM _inf1 ^sup+ , suggesting the activated natural killer cell. Next, mice were transplanted with syngeneic colon adenocarcinoma cells, and primed in vivo with OK432. These spleen cells were subsequently challenged in vitro with OK432. These spleen cells displayed a strong cytotoxic activity not only to the transplanted adenocarcinoma cells but also to other syngeneic tumor cells.     

Generation of cytolytic T lymphocytes in vitro. X. Induction of primary and secondary CTL responses by the mitogen sodium periodate.

Short-term (15 min) sodium periodate (NaIO4) treatment of mouse spleen cells previously primed in vivo or in vitro against alloantigens induced the formation of secondary (2 degree) cytolytic T lymphocytes (CTL) specific for the priming antigens. CTL formation was readily demonstrable within 24 hr after treatment.This early CTL response occurred equally well in the presence or absence of cytosine arabinoside (Ara C), indicating that NaIO4 could induce CTL independently of DNA synthesis. Forty-eight hours after periodate treatment, the lytic activity was similar to that observed in parallel cultures stimulated with irradiated allogeneic spleen cells, although the peak activity was reached earlier (day 4) and was somewhat lower than that induced by alloantigen. The addition of irradiated NaIO4-treated unprimed syngeneic spleen cells to cultures of untreated alloimmune spleen cells also led to CTL formation, which suggests an indirect mechanism of activation. In contrast to alloimmune spleen cells, normal spleen cells treated with NaIO4 developed only very low levels of cytotoxicity after 4 days of incubation. However, in the presence of PHA, such cells were capable of lysing syngeneic and allogeneic target cells.     

Immune responses against allogeneic and syngeneic tumors in aged C57BL/6 mice

Aged C57BL/6 (B6) mice could reject allogeneic BALB/c RL male 1 tumor as efficiently as young B6 mice. However, in vitro analysis showed impaired generation of cytotoxic T cell response in aged B6 mice against allogeneic tumor. The reaction could be augmented by the addition of recombinant interleukin-2 (rIL-2). Enzyme-linked immunospots (ELISPOT) produced by CD8+ T cells purified from spleen cells showed no reduction in aged mice. The findings suggested that the number of CD8+ T cells capable of reacting against allogeneic H-2 antigens was similar in young and aged B6 mice. Low cytotoxic T lymphocyte (CTL) responsiveness in aged B6 mice appeared to have resulted from low responsiveness of CD4+ T cells producing IL-2. Although CTL generation was apparently impaired, strong multiple antigenicity of allogeneic tumor evoked a rejection response in aged B6 mice. On the other hand, no rejection response was observed against syngeneic EL4 tumor in aged B6 mice even after depletion of CD4+ CD25+ immunoregulatory cells. Depletion of CD4+ CD25+ cells caused rejection of EL4 tumor in young B6 mice. The findings suggested that aged B6 mice were incapable of inducing effector cells against weak tumor antigens. Only marginal CTL response and small number of ELISPOTs were generated in young but not aged B6 mice against EL4. Addition of rIL-2 to the culture augmented EL4 killing and ELISPOTs in spleen cells from young and aged B6 mice.