The allogeneic effect on tumor growth. I. Inhibition of a murine plasmacytoma, MOPC 315, by the graft-vs-host reaction.

The allogeneic effect has been employed as a potent immunopotentiator in preventing the growth of a murine plasmacytoma and prolonging host survival. Parental BALB/c spleen cells were passively transferred to (BALB/c x A/H)F1 hybrid mice, who were then given a highly lethal dose of MOPC 315 plasmacytoma, a tumor of BALB/c origin. The resultant graft-vs-host reaction protected the recipient mice against growth of the tumor and significantly prolonged survival. This phenomenon was dependent upon the dose of BALB/c lymphoid cells employed, the route of administration, and the time interval between lymphoid cell transfer and tumor inoculation. A wide range of lymphoid cell doses and time intervals were effective, and repeated doses of allogeneic cells provided better protection than a single dose.     

A Novel Mouse Model for Multiple Myeloma (MOPC315.BM) That Allows Noninvasive Spatiotemporal Detection of Osteolytic Disease

Multiple myeloma (MM) is a lethal human cancer characterized by a clonal expansion of malignant plasma cells in bone marrow. Mouse models of human MM are technically challenging and do not always recapitulate human disease. Therefore, new mouse models for MM are needed. Mineral-oil induced plasmacytomas (MOPC) develop in the peritoneal cavity of oil-injected BALB/c mice. However, MOPC typically grow extramedullary and are considered poor models of human MM. Here we describe an in vivo-selected MOPC315 variant, called MOPC315.BM, which can be maintained in vitro. When injected i.v. into BALB/c mice, MOPC315.BM cells exhibit tropism for bone marrow. As few as 10⁴ MOPC315.BM cells injected i.v. induced paraplegia, a sign of spinal cord compression, in all mice within 3–4 weeks. MOPC315.BM cells were stably transfected with either firefly luciferase (MOPC315.BM.Luc) or DsRed (MOPC315.BM.DsRed) for studies using noninvasive imaging. MOPC315.BM.Luc cells were detected in the tibiofemoral region already 1 hour after i.v. injection. Bone foci developed progressively, and as of day 5, MM cells were detected in multiple sites in the axial skeleton. Additionally, the spleen (a hematopoietic organ in the mouse) was invariably affected. Luminescent signals correlated with serum myeloma protein concentration, allowing for easy tracking of tumor load with noninvasive imaging. Affected mice developed osteolytic lesions. The MOPC315.BM model employs a common strain of immunocompetent mice (BALB/c) and replicates many characteristics of human MM. The model should be suitable for studies of bone marrow tropism, development of osteolytic lesions, drug testing, and immunotherapy in MM.     

Antisera to the secretory component recognize the murine Fc receptor for IgA

Studies were undertaken to determine a possible structural relationship between the secretory component (SC) and the receptor for IgA (Fc alpha R). An IgA-mediated rosetting technique was used to assess the presence of Fc alpha R+ cells in various lymphoid tissues from normal BALB/c mice and mice bearing an IgA plasmacytoma (MOPC 315). Tissues from the MOPC 315-bearing BALB/c mice were found to have a significantly higher percentage of Fc alpha R+ cells; thus, nonadherent spleen cells from MOPC 315-bearing mice were used as a source of Fc alpha R+ cells in these studies. The cells were preincubated with anti-SC and then assayed for the ability of IgA to bind to the Fc alpha R. Antisera to SC from various species inhibited the formation of IgA-mediated rosettes, although preincubation of the Fc alpha R+ cells with antisera directed against other cell surface molecules (e.g., Thy1.2, Lyt1, Lyt2, Fc gamma R, MHC class I and II) or preimmune sera had no significant effect on IgA-mediated rosette formation. Preabsorption of the anti-SC with secretory IgA or with free SC removed the inhibitory effect; preabsorption with myeloma IgA had no effect. These data suggest that SC and Fc alpha R are related serologically and may be structurally related, possible in the IgA-binding region.     

Tumor-specific immunity induced by somatic hybrids. II. Elicitation of enhanced immunity against the parent plasmacytoma.

Hybrid cells derived from fusion of a BALB/c plasmacytoma (TEPC-15) and L cells (C3H origin) were used to stimulate tumor-specific immunity against the parental plasmacytoma cells. Live hybrid cells induced tumor-specific immunity against TEPC-15 more effectively than mitomycin-treated hybrid or TEPC-15 tumor cells. Adoptive transfer of immunity with spleen cells of mice immunized with hybrid cells was also more effective than that with mitomycin-treated tumor cells. The immunity induced by the hybrid cells was specific to the TEPC-15 tumor because the mice that received immune spleen cells were not protected against challenge with either HOPC-8 or McPC-603 plasmacytomas. T cell populations were primarily responsible for the transfer of specific immunity based on the sensitivity of immune cells to anti-Thy 1.2 and complement. Mice that had established solid tumors were treated with 5 x 10(7) spleen cells to evaluate the therapeutic value of the hybrid-induced immune cells. Tumors in the mice that received immune cells gradually regressed over a 40-day period, whereas tumors on the control mice continued to grow. These results suggest that a rearrangement of tumor-specific antigens on allogeneic hybrid cells can enhance their immunogenicity.     

Participation of the humoral immune system in the myeloma-specific transplantation resistance

Studies are reported that examine the participation of humoral and cellular responses in the myeloma-specific transplantation resistance induced by preimmunization of BALB/c mice with purified myeloma protein M315. A plasmacytoma spleen colony-forming assay was used to provide a quantitative estimate of the tumor immunity in recipients of unfractionated spleen cells or serum from mice immunized four to seven times with M315. The primary findings were: 1) that the tumor immunity can be transferred by immune spleen cells provided that a boost of M315 is given to adoptive hosts, and 2) that passively transferred serum containing anti-M315 idiotype antibody (a-Id315) can also inhibit tumor growth. Adoptive transfer was successful in the presence of minute amounts of a-Id315, whereas passive transfer required relatively large amounts of activity. The passive transfer experiments involved an extended injection schedule and thus could not discriminate between direct effects of antibody or idiotype-specific humoral substances on tumor cells or inductive effects on the cellular immune system. Experiments examining the properties of the immune elements involved in the transplantation immunity demonstrated that, once established, they are resistant to acute radiation (to 800 R) and cortisone damage.     

Tumor dormancy. I. Regression of BCL1 tumor and induction of a dormant tumor state in mice chimeric at the major histocompatibility complex

The growth of the BCL1 tumor in murine H-2 chimeras was studied. Lethally x-irradiated BALB/c mice were reconstituted with C57BL/6 bone marrow that had been depleted of T cells. When chimerism was established 90 to 120 days later, large doses of BCL1 cells were injected. The tumor grew progressively, reaching a peak level of as many as 10(9) tumor cells per animal by 40 days after inoculation. After that time, the tumor regressed in all the chimeric animals, and by 100 days after inoculation, virtually all the animals appeared disease free as judged by an absence of BCL1-idiotype-positive cells in the spleen and peripheral blood, a normal spleen size, and absence of an elevated white blood cell count. Such animals were followed for as long as 8 mo after tumor inoculation and remained disease free. However, transfer of graded numbers of splenocytes from these animals into normal BALB/c recipients resulted in development of tumor in recipients receiving 100 or more spleen cells. These results indicate a large tumor burden in the spleen of each donor, namely, 10(6) to 10(7) BCL1 cells. The present model should facilitate characterization of the mechanisms underlying tumor dormancy.     

Studies on the induction of tolerance to alloantigens. I. The abrogation of potentials for delayed-type-hypersensitivity response to alloantigens by portal venous inoculation with allogeneic cells

The present study investigates the effect of portal venous (p.v.) administration of allogeneic cells on the capacity of delayed-type-hypersensitivity (DTH) reactivity to alloantigens. BALB/c mice were inoculated with C3H/He spleen cells via intravenous (i.v.) or p.v. route. Intravenous injection of C3H/He spleen cells into BALB/c mice resulted in appreciable DTH responses to C3H/He alloantigens. In contrast, p.v. inoculation of the same number of C3H/He cells not only failed to induce any significant anti-C3H/He DTH responses but also abolished the capability of the animals to develop DTH responses as induced by subcutaneous (s.c.) immunization with C3H/He spleen cells. Such suppression was alloantigen-specific, since p.v. inoculation of C3H/He spleen cells resulted in selective inhibition of anti-C3H/He DTH potential without suppressing DTH responses to C57BL/6 alloantigens. This tolerance was rapidly inducible and long-lasting. When spleen cells from tolerant mice were transferred i.v. into 600 R X-irradiated syngeneic recipient mice alone or together with normal BALB/c spleen cells, these tolerant spleen cells themselves failed to induce DTH responses but did not exhibit any suppressive effect on the generation of DTH responses induced by normal spleen cells co-transferred. These results indicate that tolerance was not necessarily associated with the induction of suppressor cell activity but rather was associated with the elimination or functional impairment of clones specific for alloantigens. The results are discussed in the context of a) the role of the liver in immune responses, b) cellular mechanisms underlying the tolerance induction, and c) potential application of this approach to the future transplantation immunology.     

Cyclic AMP in plasmacytoma cells

Summary In Balb/c plasmacytoma cells (MOPC 315) the synthesis and secretion of IgA in vitro was suppressed by prior incubation of the tumor cells with anti-Balb/c alloantibody. In tumor cells so treated, the levels of cyclic AMP were found to be increased. The alloantibody, either as alloantiserum or ascitic fluid globulins from allogeneic strains of mice immunized with spleen cells, had been differentially absorbed with Balb/c spleen cells. Such absorption reduces the cytotoxic antibody effect to below detectable levels, as measured by Trypan Blue exclusion, but permits retention of substantial levels of the suppressive antibody effect. The range of dilutions of alloantibody causing the increase in cAMP corresponded with those that caused suppression of IgA secretion. When tumor cells were exposed to agents that increased the level of cAMP either endogenously or exogenously, suppression of secretion of IgA was found, similar to that caused by the alloantibody. When submaximal concentrations of suppressive antibody were combined with submaximal levels of the cAMP-increasing agents greater degrees of suppression were found, suggesting an additive effect. No cytotoxic effect on these tumor cells, as indicated by Trypan Blue exclusion, was caused by these cAMP-increasing agents at the concentrations shown, either alone or in combination with the suppressive antibody.     

Inhibition of interleukin-10 (IL-10) production from MOPC 315 tumor cells by IL-10 antisense oligodeoxynucleotides enhances cell-mediated immune responses

 Interleukin-10 (IL-10) has both inhibitory and stimulatory effects on diverse cell types of the immune system. It inhibits the antigen-presenting capacity of monocytes/macrophages and stimulates T cell proliferation. Although many tumors spontaneously release IL-10, the physiological relevance of this phenomenon to the in vivo antitumor immune response is not known. To elucidate the physiological role of tumor-released IL-10, we used IL-10-specific antisense oligodeoxynucleotides (AS-ODN) for the inhibition of IL-10 production from the tumor cells. Incubation of MOPC 315 plasmacytoma with IL-10 AS-ODN in vitro resulted in inhibition of IL-10 production and also in enhancement of the expression of major histocompatibility complex (MHC) class I, MHC class II, and B7-1 molecules. MOPC 315 cells incubated with IL-10 AS-ODN (MOPC-IL10AS) for 16 h in vitro showed reduced tumorigenicity in Balb/c mice. The mice implanted with MOPC-IL10AS effectively rejected the tumor graft, and showed strong cytotoxic T lymphocyte (CTL) activity against the parental MOPC 315 cells. In addition, MOPC-IL10AS were more effective as stimulator cells in mixed lymphocyte/tumor cell culture, and as target cells in a CTL assay. These results imply that IL-10 spontaneously released from MOPC 315 cells inhibits their immunogenicity and that the inhibition of IL-10 production by IL-10 AS-ODN may be a way to enhance the host cellular antitumor immune response. Received: 11 November 1999 / Accepted: 6 April 2000     

Some characteristics of the in vivo antitumor immunity exhibited by mice cured of a large MOPC-315 tumor by a low dose of melphalan

Summary BALB/c mice cured of a large MOPC-315 or MOPC-104E plasmacytoma following treatment with a low dose (2.5 mg/kg) of melphalan (L-PAM) were resistant to challenge with the other plasmacytoma but to a much lesser extent than to challenge with the autochthonous plasmacytoma. The resistance of the L-PAM-cured MOPC-315-tumor bearers to challenge with MOPC-104E tumor cells was increased when the MOPC-104E tumor cells were admixed with MOPC-315 tumor cells prior to their inoculation. This enhanced resistance to MOPC-104E cells was due to elimination of the MOPC-104E tumor cells through an innocent bystander killing effect since it did not render the mice more resistant to a subsequent challenge with MOPC-104E tumor cells alone. Administration of carrageenan to L-PAM-cured MOPC-315-tumor bearers 1 day after the challenge with the mixture of MOPC-104E and MOPC-315 tumor cells drastically reduced the ability of the mice to resist the tumor challenge. All of the tumors that developed in such mice were of MOPC-104E origin only (as judged by the binding specificity of the myeloma proteins secreted by the tumor cells as well as that present on their surface) even though (a) the tumor inoculum used consisted of up to 10-fold more MOPC-315 than MOPC-104E tumor cells and (b) the MOPC-315 tumor cells divide more rapidly. The same protocol of carrageenan treatment did not reduce the ability of normal BALB/c mice to develop in vivo a primary cell-mediated cytotoxic response nor a primary antibody response indicating that it has no effect on the initiation of an immune response. Therefore, it is conceivable that carrageenan treatment reduced the ability of L-PAM-cured MOPC-315-tumor bearers to reject a challenge with MOPC-315 and MOPC-104E tumor cells by interfering at the effector stage. The ability of the L-PAM-cured MOPC-315-tumor bearers to reject the MOPC-315 cells present in the challenge mixture was reduced when the mice were treated with anti-Thy 1.2 antibody but not with carrageenan, indicating that T-cells independent from carrageenansensitive effector cells are required for the rejection of the MOPC-315 tumor cells. Thus, at least two different effector mechanisms participate in the rejection of a challenge composed of MOPC-315 and MOPC-104E tumor cells by L-PAM-cured MOPC-315-tumor bearers. One of the mechanisms is dependent on the action of carrageenansensitive effector cells while the other does not require carrageenan-sensitive effector cells but is T-cell-dependent.Supported by Research Grant IM-435 from the American Cancer Society and Research Grant CA-35761 from the National Cancer InstituteIn partial fulfillment of the requirements for the Doctor of Philosophy degree     

Augmentation of syngeneic tumor-specific immunity by semiallogeneic cell hybrids

Hybrid cell lines were established from fusions between lipopolysaccharide- (LPS) stimulated C57BL/6J spleen cells and MPC-11 tumor cells (45.6TG1.7, abbreviated M45), and were tested for their ability to immunize semiallogeneic mice against a parental tumor challenge. These hybrids were tumorigenic in syngeneic (BALB/c X C57BL/6J) F1 (CB6F1) mice but did not grow in semiallogeneic (BALB/c X A/J) F1 (CAF1) mice. All hybrids express both parental major histocompatibility antigens (H-2b and H-2d) as detected by indirect immunofluorescence and by their ability to function as either stimulators or targets for allogeneic cytotoxic lymphocytes (CTL). M45 tumor-associated antigens (TAA) were expressed on the hybrid surface as shown by their ability to act as either stimulators or targets for syngeneic CTL specific for M45 TAA. Immunization of semiallogeneic CAF1 mice with the hybrids i.p. followed by a challenge with M45 tumor cells resulted in extended survival when compared to untreated mice or animals immunized i.p. with M45 tumor cells. This immunity was specific and was not due to an allogeneic effect; immunization with an unrelated H-2bd tumor, 70Z/3, or H-2bd B6D2F1 spleen cells or with semiallogeneic spleen cells plus M45 did not protect mice from M45 challenge. Interestingly, prophylactic priming with semiallogeneic hybrid tumor cells or parental myeloma cells led to M45-specific CTL and "help" for an in vitro CTL response; however, the degree of CTL priming by hybrid tumors was not augmented when compared to the level of CTL achieved with parental tumor alone. Hence, stimulation of CTL activity per se by hybrid tumor cells cannot explain the protective effect of hybrid tumor immunization. These studies nevertheless confirm that semiallogeneic hybrids, which we show express TAA and alloantigens, can be used to immunize mice against a lethal syngeneic myeloma tumor challenge.     

Eradication of a large MOPC-315 tumor in athymic nude mice by chemoimmunotherapy with Lyt2+ splenic T cells from melphalan-treated BALB/c mice bearing a large MOPC-315 tumor

Summary We have previously shown that spleen cells from BALB/c mice that are in the process of eradicating a large MOPC-315 tumor following low-dose (2.5 mg/kg) melphalan (l-phenylalanine mustard) therapy are effective in preventing tumor progression upon adoptive transfer into BALB/c mice bearing a barely palpable tumor that had been treated with a subcurative dose of melphalan [Mokyr et al. (1989) Cancer Res 49: 4597]. Here we show that such spleen cells in conjunction with a subcurative dose of drug (adoptive chemoimmunotherapy, ACIT) can cause the complete regression of a large (15–20 mm) s.c. MOPC-315 tumor in a large percentage of T-cell-deficient (athymic nude) tumor-bearing mice. Spleen cells that were effective in ACIT of athymic nude mice displayed in vitro a substantial direct lytic activity against MOPC-315 tumor cells, and the lytic activity was greatly enhanced when the spleen cells were cultured for 5 days with or without mitomycin-C-treated MOPC-315 stimulator tumor cells. The cells responsible for the therapeutic effectiveness of the spleen cells in ACIT of athymic nude mice, as well as the cells responsible for the direct in vitro anti-MOPC-315 lytic activity of the spleen cells, were of the Lyt 2 and not the L3T4 phenotype. Most of the athymic nude mice that completely eradicated a large MOPC-315 tumor as a consequence of ACIT were capable of rejecting a challenge with 30–100 times the minimal lethal tumor dose for 100% of normal BALB/c mice administered more than 1 month after the ACIT. The ability of these athymic nude mice to resist the tumor challenge was associated with the presence of a greatly elevated percentage of cells expressing T cell surface markers in their spleens. Thus, it is conceivable that splenic Lyt 2⁺ T cells from melphalan-treated BALB/c mice bearing a large MOPC-315 tumor mediate their therapeutic effectiveness in ACIT of athymic nude mice bearing a large MOPC-315 tumor, at least in part, through direct cytotoxicity for MOPC-315 tumor cells. In addition, eradication of a large MOPC-315 tumor through cooperation between antitumor immunity and melphalan toxicity endues the athymic nude mice with an elevated percentage of T cells in their secondary lymphoid organs, and these T cells are probably responsible for the long-lasting protective antitumor immunity exhibited by these mice.Supported by research grant IM-435A from the American Cancer Society and research grant B-8806 from the Bane EstateIn partial fulfillment of the requirements for the Doctor of Philosophy DegreeRecipient of Career Development Award CA-01350 from the National Cancer Institute     

Suppression of growth of a mouse plasmacytoma by the IgG2 fraction of syngeneic antitumor globulin

Summary The effects of syngeneic antitumor antibody on transplanted plasmacytoma cells have been examined. Globulin was prepared from ascites fluids produced in Balb/c mice injected with MOPC 315 tumor cells and bearing the solid tumor. Normal Balb/c mice were given inoculations of tumor cells that had been incubated with the antitumor globulin obtained at various intervals after immunization, or with portions of such globulins. These materials were prepared to express the IgG2 class antibody by three procedures: precipitation with heterologous anti-mouse IgG1, passage through columns of Sepharose anti-IgG1, or adsorption to and elution from heat- and formalin-killed protein A-bearing staphylococci. The original antitumor globulins showed differences with time relative to the second injection of the immunizing tumor, in that a number of the earlier pools led to some suppression of tumor growth, and a number of the later pools led to some enhancement. Of the globulins obtained later, preparations expressing the IgG2 class of antibody by precipitation with anti-IgG1 serum caused some suppression of tumor growth. Pronounced suppression of growth was consistently obtained with anti-MOPC 315 globulin freed of IgG1 by passing it through an anti-IgG1 immunoadsorbent, and with IgG2a preparations obtained by elution from the protein A-bearing staphylococci. Of the anti-IgG1 column-treated preparations, the suppressive effect was maximal in globulin obtained 15–26 days after the second immunization. The suppressive effect of these preparations could be removed by absorption with MOPC 315 cells, but not by cells of another Balb/c tumor nor by two other plasmacytomas.     

Studies on the induction of tolerance to alloantigens. II. The generation of serum factor(s) able to transfer alloantigen-specific tolerance for delayed-type hypersensitivity by portal venous inoculation with allogeneic cells

The administration of C3H/He spleen cells into allogeneic BALB/c mice via portal venous (p.v.) route resulted in C3H/He alloantigen-specific tolerance for delayed-type hypersensitivity (DTH) responses. When serum from these tolerant BALB/c mice were transferred into naive syngeneic BALB/c mice, the recipient mice lost the capability of generating DTH responses as induced by s.c. immunization with C3H/He cells. Tolerance was transferred only by serum from BALB/c mice inoculated p.v. with C3H/He cells, but not by serum from C3H/He mice inoculated p.v. with C3H/He cells, or BALB/c mice inoculated i.v. with C3H/He cells. This tolerogenic activity in serum from p.v. inoculated BALB/c mice was C3H/He alloantigen specific, because the transfer of the serum did not interfere with the development of anti-C57BL/6 DTH responses in recipient BALB/c mice. Such a serum factor(s) was inducible as early as 1 wk after the inoculation of C3H/He cells into BALB/c mice and not associated with anti-C3H/He alloantibody activity. Moreover, anti-C3H/He or C57BL/6-specific tolerogenic factor(s) prepared in the respective BALB/c or C3H/He mice was successfully transferred into totally allogeneic recipient mice, indicating no requirement of H-2, as well as non-H-2 restriction for the function of serum tolerogenic factor(s). Thus this study demonstrates that p.v. inoculation of allogeneic cells generates serum factor(s) able to transfer in H-2 and non-H-2-unrestricted manners the in vivo tolerance of the alloreactivity specific for alloantigens used for p.v. inoculation.     

Cure of mice bearing a late-stage,highly metastatic,drug-resistant tumor by adoptive chemoimmunotherapy

We show here that in contrast to BALB/c mice bearing a late-stage, large MOPC-315 plasmacytoma, BALB/c mice bearing a late-stage, large RPC-5 plasmacytoma were not cured by cyclophosphamide therapy (15, 50, 100 or 200 mg/kg). However, most BALB/c mice bearing a late-stage RPC-5 tumor were cured by cyclophosphamide therapy (100 mg/kg) in conjunction with adoptive immunotherapy using tumor-infiltrated spleen cells (TISpC) that had been cultured with inactivated RPC-5 tumor cells plus polyethylene glycol 6000, even though this protocol was not effective for the therapy of mice bearing a barely palpable, early-stage RPC-5 tumor. Only a few of the mice that were cured of a late-stage RPC-5 tumor following adoptive chemoimmunotherapy (ACIT) were resistant to a subsequent challenge with RPC-5 tumor cells. However, the challenged mice that had developed progressively growing tumors could then be cured by cyclophosphamide alone when the tumor became large, even though this treatment was not curative for mice bearing a tumor of similar size but not previously treated by ACIT. Thus, the cure by ACIT of BALB/c mice bearing a lethal, late-stage RPC-5 tumor with extensive metastases provides a novel experimental tumor model for investigating the mechanisms by which a chemotherapeutic drug and adoptive cellular immunotherapy can cooperate in causing the complete regression of a large tumor load.Supported by research grant CA-30088 from the National Cancer Institute and IM-435 from the American Cancer Society. M. B. M. was supported by Career Development Award CA-01350 from the National Cancer InstituteThis work is a partial fulfillment of the requirements for the Ph.D. degree     

T-cell neoplasm induced by subcutaneous transplantation of a plasmacytoma: characterization of tumor cells.

Thymocytes, isolated 6 days following subcutaneous (sc) transplantation of BALB/c MOPC-315 plasmacytoma into F₁ (BALB/c × C57BL) hybrid mice, when injected sc into normal syngeneic mice, caused the development of a solid sc tumor. The cells of the newly developed tumor were of a mixed population of θ⁺F₁ (BALB/c × C57BL) and θ^? BALB/c cells (approximately 1:1), which represents a new type of mixed T cell-plasma cell neoplasm. Efforts were made to isolate the transformed thymocytes (θ⁺) from the plasmacytoma (θ^?) cells in the new tumor, exploiting differences in their surface properties. Treatment of the mixed tumor cell population with peanut agglutinin (PNA) revealed that only the T tumor cells were agglutinated. The agglutinated cells were recovered after dispersing the clumps with d-galactose (0.15 M) and consisted of 95% θ⁺ cells. The PNA-agglutinated cells were found to induce a similar tumor (85% θ⁺ cells) when injected sc into F₁ (BALB/c × C57BL) mice.     

Reversal by the MER tubercle bacillus fraction of the suppressive effects of heterologous antilymphocytic serum (ALS) on the allograft reactivity of mice

Treatment of immunized C57B1 mice with the MER fraction of BCG prevented wholly or in large part the strong immunosuppressive effects elicited by heterologous ALS against allograft reactivity, as measured by the in vitro cytotoxic activity of spleen cells against the immunizing allogeneic cells (a BALB/c plasmacytoma). Moreover, the heightened cytotoxic capacity of spleen cells bestowed by treatment of the donor with MER was manifested in some instances despite exposure to ALS. Spleen cells from MER-treated hosts were also more refractory to the direct cytotoxic action of ALS and complement in vitro.     

A murine plasmacytoma MOPC 104E resistant to cyclophosphamide is resistant to immunotherapy

Summary A murine plasmacytoma MOPC 104E (MOPC) is highly sensitive to chemotherapeutic agents such as cyclophosphamide and mitomycin C as well as to immunotherapy (OK-432-combined adoptive immunotherapy using interleukin-2-cultured killer cells). In the present study, we prepared cyclophosphamide-resistant MOPC cells (MOPC-CPA/R) by serial in vivo passage of tumor cells following cyclophosphamide treatment. The in vivo sensitivity of MOPC-CPA/R to mitomycin C or to immunotherapy (OK-432-combined adoptive immunotherapy) was significantly decreased compared to the parent MOPC. In vitro experiments showed that MOPC-CPA/R were more resistant (five-fold) to lysis by cultured immune spleen cells than MOPC. Inhibition of the lytic activity of cultured immune spleen cells against MOPC was significantly increased (P <0.05) by the addition of unlabeled MOPC compared to unlabeled MOPC-CPA/R. These results suggest that MOPC-CPA/R express weaker antigenicity than MOPC. However, the transfer of immune spleen cells cultured with tumor extract derived from MOPC-CPA/R significantly prolonged the survival of MOPC-CPA/R-inoculated mice. Thus, by repeated cyclophosphamide treatment, tumor cells with low-antigenicity were selected. These tumor cells had lower sensitivity to another chemotherapeutic agent and immunotherapy. Such an immunological response may play an important role in cancer therapy.     

Young F mice spontaneously generate cytotoxic T cells against parental targets.

Spleen cells from young (AKR/J female x BALB/c) or (BALB/c female x AKR/J)F1 mice can spontaneously generate effector cytotoxic T lymphocytes (CTL), in a 5-day primary in vitro culture, which lyse target cells from AKR/J and BALB/c but not allogeneic mice. These spontaneous CTL responses first appear when spleen cells are taken from F1 mice at 3 to 4 weeks of age, are maximum at about 5 weeks, and have declined by week 7. The fact that these spontaneous CTL responses are never detectable in the spleen cell cultures from any ages of parental AKR/J and BALB/c mice makes them unique properties of the F1 mice.     

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.