Multiple splenic lymphoid cell subpopulations regulate H-2 antigen expression on teratocarcinoma cells in vivo

Undifferentiated murine 402AX teratocarcinoma cells do not express MHC antigens when passaged in vitro or in vivo in genetically susceptible host mice. When passaged in vivo in genetically resistant mice, however, the tumor cells become H-2b antigen positive regardless of the H-2 haplotype of the resistant host mouse. The present studies use monoclonal anti-H-2b antibodies to corroborate these earlier findings, which were performed with conventional antisera. Previous studies have established that host bone marrow plus lymphoid cells from resistant primed donors regulate tumor cell H-2b antigen expression. Using bone marrow and mature lymphoid cell reconstitution techniques, the present studies indicate that splenic Ig- cells from genetically resistant host mice are the most efficient lymphoid cell subpopulation in tumor cell H-2b antigen induction. Ig+ spleen cells also reconstitute the capacity to induce teratocarcinoma cell H-2 antigens but are less effective than Ig- spleen cells. Tumor cell H-2 antigen induction in C57BL/6 beige mice is impaired compared to C57BL/6 hosts, which suggests that host NK cells may also be involved in tumor cell H-2 antigen induction. Reconstitution of lethally irradiated resistant hosts for teratocarcinoma cell H-2 antigen expression requires bone marrow plus resistant primed lymphoid cell subpopulations; bone marrow alone is insufficient. These results indicate that multiple splenic lymphoid cell subpopulations requiring a radiosensitive host environment and/or factor for differentiation regulate teratocarcinoma 402AX H-2b antigen expression in vivo in genetically resistant mice.     

Transfection and expression of syngeneic H-2 genes does not reduce malignancy of H-2 negative teratocarcinoma cells in the autologous host

Rejection of the MHC class I negative 402AX teratocarcinoma is accompanied by induction of tumor cell-encoded H-2K and H-2D antigens by the genetically resistant host. To determine whether MHC antigen expression is required for 402AX rejection, we have prepared H-2Db-transfected 402AX cells (402AX/Db). Transfectants express high levels of H-2Db, most of which is not associated with beta 2-microglobulin. MHC syngeneic and allogeneic mice susceptible to 402AX are resistant to 402AX/Db, suggesting that MHC class I antigen expression is required for tumor rejection. Autologous 129 hosts, however, are susceptible to 402AX/Db. 402AX cells transfected with the H-2Kb gene (402AX/Kb) are also lethal in the autologous 129/J host, but rejected by MHC syngeneic and allogeneic mice. Non-129 strain 402AX-susceptible mice pre-immunized with 402AX/Db or simultaneously challenged with 402AX/Db plus 402AX are immune to 402AX. Mice immunized with 402AX/Db produce MHC class I induction factor. 402AX/Db and 402AX cells are lysed equally by natural killer cells, indicating that in 402AX cells the expression of class I antigens is unrelated to NK susceptibility. These studies confirm the requirement for class I expression in 402AX immunity, but demonstrate that in the autologous host immunity requires additional factors beyond class I antigen expression.     

402AX teratocarcinoma MHC class I antigen expression is regulated in vivo by Lyt 1, Lyt 2, and L3T4 expressing splenic T cells

The murine 402AX teratocarcinoma is a MHC class I antigen negative tumor of 129 strain origin. Host resistance to the 402AX tumor is genetically controlled. When passed intraperitoneally in genetically resistant mice, the tumor cells are induced to express MHC Class I antigens of the 129 genotype. When passed in genetically susceptible mice, the tumor cells remain MHC class I antigen negative. Earlier studies have demonstrated that resistance to the tumor and regulation of tumor cell MHC class I antigen expression are under the control of the host's immune system. The present studies indicate that splenic Lyt 1-, Lyt 2-, and L3T4-expressing cells regulate tumor cell MHC class I antigen expression, and that these cells require a genetically resistant host environment in which to differentiate. Splenic T cells primed to the 402AX tumor and transferred into genetically susceptible 129 mice give rise to GVHD, suggesting that immunity to the tumor involves reactivity to 129 minor histocompatibility antigens.     

Resistance to 402AX teratocarcinoma involves immunity to minor histocompatibility antigens

The 402AX teratocarcinoma is a 12/J-derived mouse major histocompatibility complex (MHC) antigen negative tumor that is induced to express H-2^b class I antigens during rejection. Resistance to 402AX by MHC allogeneic and syngeneic mice is immunologically mediated and involves the recognition of tumor-associated antigens (TAA) in the context of induced MHC class I antigens. The current studies were undertaken to define the 402AX TAAs. Reconstitution of irradiated susceptible hosts (129/J) with 402AX-primed resistant spleen cells (C57BL/6) results in acute graft-versus-host disease, suggesting that tumor-primed C57BL/6 splenocytes are reactive to tumor genotype (129/J) minor histocompatibility (Hm) antigens. C57BL/6 anti-129/J effector cells, although not directly cytotoxic for 402AX cells, are specifically cold target inhibited by 402AX cells. Genetically susceptible hosts (C3H.SW) immunized to 129/J Hm antigens by skin grafting become resistant to an i.p. challenge of 402AX cells. These results suggest that 129/J Hm antigens may be the TAAs recognized during genetically controlled rejection of the 402AX teratocarcinoma.     

The unique killing of embryo-derived teratocarcinoma cells by nonactivated murine macrophages is not due to a lack of H-2 antigen expression.

It is well documented that activated macrophages, but not nonactivated ones, kill tumor cells in vitro without damaging normal cells. We, however, have previously shown that embryo-derived teratocarcinoma cells (F9, P19, PCC4) are efficiently killed by nonactivated macrophages as well as by activated ones. Whereas other tumor cells are killed extracellularly by macrophages, we found that F9 teratocarcinoma cells are phagocytosed alive by macrophages and subsequently killed intracellularly by a process dependent on intact lysosomal function. Neither the H-2 antigens nor the mRNAs for the alpha-chain and beta 2-microglobulin are detectable in embryo-derived teratocarcinoma cells. An obvious explanation for this unique killing is that the nonactivated macrophages recognize and kill these cells due to their lack of class I MHC antigen expression, assuming that class I MHC gene products on the target cells switch off the cytolytic machinery of nonactivated macrophages. Our present findings demonstrate that there is no correlation between H-2 antigen expression on tumor cells and their susceptibility to killing by macrophages. Retinoic acid-differentiated F9 cells and P19 cells expressing H-2 antigen after exposure to MAF (IFN-gamma) were sensitive to the killing by nonactivated macrophages. Hybrids that arose from fusion of P19 teratocarcinoma cells with embryonal normal fibroblasts (C57BL/6), which displayed the morphology of embryonal carcinoma stem cells and expressed H-2 antigens, were also sensitive to the killing by nonactivated macrophages. On the other hand, the H-2-negative testicular 402AX teratocarcinoma cells and K1735P melanoma cells were both resistant to the killing by nonactivated macrophages. We concluded that the unique killing of embryo-derived teratocarcinoma cells by nonactivated murine macrophages is not related to a lack of H-2 antigen expression.     

Induction of glial cell MHC antigen expression in neurotropic coronavirus infections. Characterization of the H-2-inducing soluble factor elaborated by infected brain cells

Neurotropic coronavirus (mouse hepatitis virus strain A59) infection induces major histocompatibility complex class I (H-2) surface antigens on oligodendrocytes and astrocytes, cells that do not normally express detectable MHC antigens on their surface. The induction on MHC antigen expression potentially allows immunocytes to interact with infected glial cells and may play a critical role in the development of virus-induced, immune-mediated demyelination in the central nervous system, a possible model of human multiple sclerosis. In this study, we characterized the soluble factor involved in MHC antigen induction, quantitated induction of MHC antigens, and analyzed the central nervous system cell type involved in the production of the factor. The H-2-inducing factor, most likely produced by astrocytes, was found to be nondialyzable, heat- and trypsin-sensitive, but resistant to treatment at pH 2.0. The m.w. of the factor was estimated as 50 to 100 kDa. Studies on fractionation by ultrafiltration and sucrose density gradient along with antibody-blocking experiments indicate that the factor is not interferon or virus particles.     

Mouse Hepa-1 tumor is rejected by H-2Db-restricted CTL despite decreased MHC class I antigen expression

It has recently been hypothesized that tumor cells with reduced levels of MHC class I antigens are more susceptible to NK-mediated lysis and are rejected by NK cells, whereas tumor cells with normal levels of class I are rejected by tumor-specific CTL. We have tested this hypothesis using a mouse hepatoma system. The Hepa-1 tumor is a spontaneous H-2Kb loss variant that arose from the BW7756 tumor, when BW7756 was adapted to growth in culture. Our studies have shown that despite the loss of H-2Kb antigen, Hepa-1 is not more susceptible to NK lysis than its H-2Kb-transfected variants. These studies also suggested that NK cells were not responsible for rejection of the Hepa-1 tumor. The Hepa-1 tumor, therefore, appears to contradict the hypothesized linkage of MHC levels and NK susceptibility. Because NK cells are not involved in immunity to this tumor, we have sought to identify the effector cell responsible for Hepa-1 rejection. Cytotoxic T lymphocyte assays demonstrate that in vitro, Hepa-1 cells are lysed by Hepa-1-specific H-2Db-restricted CD4-CD8+ T lymphocytes. Footpad assays demonstrate that in vivo, Hepa-1 rejection requires CD4+CD8- and CD4-CD8+ Hepa-1-primed splenocytes. These results indicate that immunity to Hepa-1 is T cell mediated. Hepa-1 is therefore an example of an unusual tumor in that down-regulation of MHC class I antigen expression is associated with increased CTL susceptibility.     

Autocrine induction of major histocompatibility complex class I antigen expression results from induction of beta interferon in oncogene-transformed BALB/c-3T3 cells.

By varying growth conditions, we identified a novel mechanism of autocrine regulation of major histocompatibility complex (MHC) class I gene expression by induction of beta interferon gene expression in transformed BALB/c-3T3 cells. Low-serum conditions enhanced MHC class I antigen expression in v-rasKi- and v-mos-transformed BALB/c-3T3 cells but not in untransformed BALB/c-3T3 cells. Transformed and untransformed cells grown under standard serum conditions (10% bovine calf serum) expressed similar cell surface levels of MHC class I antigens. However, low-serum conditions (0.5% bovine calf serum) induced four- to ninefold increases in cell surface levels of MHC class I antigens in both v-rasKi- and v-mos-transformed cells but not in untransformed cells. These increases in MHC class I gene expression were seen at both the mRNA and cell surface protein levels and involved not only the heavy-chain component of the class I antigens but also beta 2 microglobulin. Beta 1 interferon mRNA and beta interferon-inducible 2',5'-oligoadenylate synthetase mRNA were induced by growth under low-serum conditions in transformed BALB/c-3T3 cells, and antibodies to beta interferon blocked the induction of MHC class I antigen expression by serum deprivation in these cells. These results demonstrate that growth under low-serum conditions leads to induction of beta interferon expression in oncogene-transformed cells which then directly mediates autocrine enhancement of MHC class I gene expression.     

Soluble factors produced during an immune response regulate Ia antigen expression by murine adenocarcinoma and fibrosarcoma cells

LT-85 is an alveologenic adenocarcinoma of C3Hf/HeN mice. Comparisons of the in vitro and in vivo surface properties of these cells revealed that under normal conditions, they expressed I-A and I-E antigens iv vivo only. By using clonally derived cells, it was established that this phenomenon was not due to the selection of an Ia antigen-positive tumor cell subpopulation, but resulted from phenotypic conversion of Ia antigen-negative tumor cells. These tumor cells and 1053 cells (a fibrosarcoma of C3H/HeN MTV- mice) could, however, be induced to express I-A, I-E, and much higher levels of H-2 antigens in vitro by co-culturing them with spleen cells from LT-85 tumor-bearing C3H/HeN MTV- mice. In vitro induction of Ia and H-2 antigens did not result from contaminating splenocytes or from antigen transfer, because splenocytes from BALB/c (H-2d) mice immunized with A/J (H-2k/d) cells were able to induce the expression of Iak antigens by both tumor cell lines. It was found that this phenomenon was neither H-2-restricted nor antigen-specific. The results clearly indicated, however, that an immune response was required to generate phenotypic conversion of the tumor cells, both in vivo and in vitro. It was further found that soluble, rather than cellular, factors produced during an immune response induced the expression of Ia antigens by LT-85 and 1053 tumor cells. In contrast to what has been reported about the induction of Ia antigens on macrophages and normal epithelial and endothelial cells, the induction of Ia antigens on LT-85 and 1053 cells did not appear to require T cells, and did not involve gamma-interferon. These findings demonstrate that some tumor cells are capable of altering their MHC antigen phenotype in response to factors produced during an immune response in vivo or in vitro. Because of the involvement of Ia antigens in several aspects of immune phenomena, the ability of tumor cells to differentially express Ia antigens in response to environmental factors may have profound effects on host-tumor interactions. Furthermore, the differences seen in the phenotypes of tumor cells grown in vitro and in vivo suggest that in vitro methodologies of tumor cell characterization may not present a complete picture of the natural state of the tumor cell surface.     

Rejection of allogeneic tumor is not determined by host responses to MHC class I molecules and is mediated by CD4-CD8+ T lymphocytes that are not lytic for the tumor

In previous studies, the murine SaI (A/J derived, KkDd) sarcoma was transfected with the allogeneic MHC class I H-2Kb gene, and expressed high levels of H-2Kb antigen. Contrary to expectations, the tumor cells expressing the alloantigen (SKB3.1M tumor cells) were not rejected by autologous A/J mice. Because these results contradict the laws of transplantation immunology, the present studies were undertaken to examine the immunogenicity of SKB3.1M and SaI cells in allogeneic hosts. Similar to SKB3.1M, SaI cells are lethal in some allogeneic strains, despite tumor-host MHC class I incompatibilities. Tumor challenges of SKB3.1M and SaI cells, however induce MHC class I-specific antibodies and CTL in both tumor-resistant and -susceptible hosts. Although the tumors induce specific CTL, tumor cells are not lysed in vitro by these CTL, suggesting that the tumor cells are resistant to CTL-mediated lysis. Since growth of these tumors does not follow the classical rules of allograft transplantation, and because the tumor is not susceptible to CTL-mediated lysis, we have used Winn assays to identify the effector lymphocyte(s) responsible for SaI rejection. Depletion studies demonstrate that the effector cell is a CD4-CD8+ T lymphocyte. Collectively these studies suggest that the host's response to MHC class I alloantigens of SKB3.1M and SaI cells does not determine tumor rejection, and that effector cells other than classically defined CTL, but with the CD4-CD8+ phenotype, can mediate tumor-specific immunity.     

Simian immunodeficiency virus induces expression of class II major histocompatibility complex structures on infected target cells in vitro

The human immunodeficiency virus (HIV) and the closely related simian immunodeficiency virus (SIV) induce profound immune dysfunction in primate species. The present studies show that cell populations infected in vitro with SIV exhibit increases in major histocompatibility complex (MHC) class II antigen expression. Cell lines chronically infected with both the monkey and human viruses express substantially more MHC class II but not more lineage-restricted or activation antigens on their membranes than do uninfected cell lines. Furthermore, 2'-deoxy-5-iodouridine increased MHC class II antigen expression on SIV-infected cell lines in parallel with increased expression of viral antigens. MHC class II induction does not appear to be mediated through the production of a soluble factor, such as gamma interferon, by SIV-infected cells. Interestingly, studies of the kinetics of antigen expression by cell lines after SIV infection indicate that the induction of MHC class II structures is a late event. Immunoelectron microscopy revealed that MHC class II antigen is expressed not only on the surfaces of the SIV-infected cells but also on the envelope of virus particles derived from those cells. MHC antigen expression on virus-infected cells and the expression of those determinants by the virus may play a role in the pathogenesis of acquired immunodeficiency syndrome and the autoimmune abnormalities observed in HIV-infected individuals.     

Expression of antigen on mature lymphocytes is required to induce T cell tolerance by gene therapy

Expression of a retrovirally encoded allogeneic MHC class I gene in bone marrow-derived cells can be used to induce tolerance to the product of the retrovirally transduced gene. In this work we examined whether expression of a retrovirally transduced allogeneic MHC class I gene in bone marrow-derived cells from recombinase-activating gene-1 (RAG-1)-deficient mice was sufficient to induce tolerance when transplanted into conditioned hosts together with bone marrow from MHC-matched wild-type mice. Reconstitution of mice with either MHC-matched RAG-1-deficient or wild-type bone marrow transduced with the allogeneic MHC class I gene H-2K(b) led to long-term expression of K(b) on the surface of bone marrow-derived hematopoietic lineages. T cells from mice reconstituted with H-2K(b)-transduced wild-type bone marrow were tolerant to K(b). In contrast, expression of K(b) in the periphery of mice reconstituted with a mixture of retrovirally transduced RAG-1-deficient bone marrow and mock-transduced wild-type bone marrow fell below detectable levels by 4 wk after transplantation. T cells that developed in these mice appeared to be hyporesponsive to K(b), demonstrating that expression of K(b) on bone marrow-derived APCs was not sufficient to induce tolerance. Our data suggest that induction of tolerance in molecular chimeras requires expression of the retrovirally transduced allogeneic MHC Ag on the surface of mature lymphocytes that populate the host thymus.     

The influence of major histocompatibility complex class I antigens on tumor growth and metastasis

The work described here demonstrates the importance of major histocompatibility complex class I antigens for the control of tumor growth and metastasis by the host's immune system. In certain murine tumor cells which have lost expression of H-2 class I antigens, a de novo expression of H-2 can be achieved by transfection with syngeneic class I genes. In contrast to the parental cells the transfected tumors do not grow any more in syngeneic mice, or in other cases they do not form metastases. The studies suggest that the de novo expression of the H-2 antigens renders the tumors highly immunogenic and leads to effective recognition of a tumor-associated antigen in conjunction with the transfected H-2 antigen. These conclusions were confirmed in other tumor systems. For example, separation of a heterogeneous tumor into clones expressing high or low amounts of H-2 showed that only the tumor cell with low H-2 grew well in syngeneic mice, whereas the H-2 high tumor clones were rejected. In other studies in vitro induction by IFN-gamma of H-2 antigen on H-2 negative tumors led to reduced tumor growth in vivo which was due to the increased immunogenicity. About 10% of human tumors are also low or defective for HLA class I expression and often these tumors appear to be more malignant. The class I negative tumors could either have arisen from class I low or negative tissues or are HLA loss variants which escaped the attack of the immune system. Altogether, our studies and the data of other laboratories demonstrate the important role of class I antigens for anti-tumor immunity and they suggest that modulation of class I expression by gene transfection or by induction with soluble mediators could be a useful tool for the manipulation of tumor immunity.     

Introduction of the interferon γ gene into mouse T lymphoma cells with low MHC class I-expression results in selective induction of H-2Dk and concomitant enhanced metastasis

 Interferon-γ(IFNγ)-induced up-regulation of MHC class I expression on tumor cells can induce a potent CD8-mediated antitumor response. Consequently, many investigators have proposed IFNγ gene transfection as a means to immunogenize tumor cells and to vaccinate against metastatic disease. In this study, we demonstrate that transfection of the IFNγ gene in a BW5147 variant (LiD^lo) with low MHC class I expression results in a selective induction of H-2D^k but unaltered H-2K^k expression. In earlier reports we demonstrated a positive correlation between H-2D^k expression and enhanced metastatic potential of BW variants. In accordance with these observations, we observed that intravenous inoculation of LiD^lo(IFNγ) variants into syngeneic AKR mice led to enhanced metastasis as compared to parental LiD^lo and LiD^lo(neo) control transfectants. Tumor cells, derived from local subcutaneous tumors or sporadic metastases from mice inoculated with LiD^lo tumor cells, were found to up-regulate H-2D^k selectively. Anti-asialoGM1 treatment of AKR mice allowed rapid experimental metastasis formation by the LiD^lo and LiD^lo(neo) variants, indicating that natural killer (NK) cells control the metastatic behavior of these tumor cells. This was corroborated by in vitro cytotoxicity experiments, demonstrating that LiD^lo and LiD^lo(neo) tumor cells were NK-sensitive, while the BW IFNγ transfectants became resistant to lymphokine-activated killer cells and poly(I)·poly(C)-induced NK cells. We thus conclude that (a) IFNγ up-regulates selectively the MHC class I antigen H-2D^k, (b) H-2D^k governs susceptibility towards NK cells, and (c) NK susceptibility determines the experimental metastatic behavior of BW tumor cells. Received: 2 May 1996/Accepted: 21 May 1996     

MHC antigen expression by melanomas recovered from mice treated with allogeneic mouse fibroblasts genetically modified for interleukin-2 secretion and the expression of melanoma-associated antigens

Recent approaches toward the immunotherapy of neoplastic disease involve the introduction of expression-competent genes for interleukin-2 (IL-2) into autologous malignant cells. Treatment of tumor-bearing experimental animals with the IL-2-secreting cells successfully induces partial and at times complete remissions. In most instances, however, although delayed, progressive tumor growth continues. Here, certain of the characteristic of B16 melanomas (H-2^b) persisting in C57BL/6 mice (H-2^b) treated with an IL-2-secreting, melanoma-antigen-positive cellular immunogen (RLBA-IL-2 cells) are described. Unlike the melanoma cells first injected, B16 cells recovered from mice treated with RLBA-IL-2 cells were deficient in the experssion of MHC class I, but not class II determinants. Deficient MHC class I expression correlated with the cells' resistance to cytotoxic T lymphocytes (CTL) from the spleens of mice immunized with RLBA-IL-2 cells. Melanomas persisting in mice treated with non-IL-2-secreting, melanoma-antigen-positive cell constructs (RLBA-ZipNeo cells) were also deficient in the expression of MHC class I determinants, and the melanoma cells were resistant to CTL from mice immunized with RLBA-ZipNeo cells. Thus, the expression of melanoma-associated antigens rather than IL-2-secretion correlated with deficient MHC class I expression by the persistent melanomas. This point was substantiated by the expression of MHC class I antigens by melanomas persisting in mice treated with IL-2-secreting, melanoma-antigen-negative LM cells (LM-IL-2); it was equivalent to that of melanomas in untreated mice. The involvement of MHC class I antigens in the immune resistance of persistent melanoma cells from mice treated with the melanoma-autigen-positive immunogens was indicated by the effect of interferon (IFN) orN-methyl-N-nitro-N-nitrosoguanidine (MNNG) on the susceptibility of the cells to anti-melanoma CTL. Treatment of the resistant melanomas with IFN or MNNG stimulated MHC class I antigen expression and restored the cells' sensitivity to CTL from mice immunized with IL-2-secreting or nonsecreting, melanoma-antigen-positive cellular immunogens. Prior treatment of the treated cells with antibodies to MHC class I determinants inhibited the cells' susceptibility to CTL from mice immunized with RLBA-IL-2 cells.     

Immune responses to weakly immunogenic virally induced tumors. III. Genetically unrestricted cytolysis of allogeneic tumor target cells.

Splenocytes from A mice injected with YAC-1 or RBL5 could generate, after in vitro culture with or without stimulation, a genetically nonrestricted cytotoxic response against the allogenic tumor RBL5. YAC-1 tumor is an in vitro carried tumor induced in A mice (H-2a) by Moloney virus. RBL5 tumor is a Rauscher virus-induced tumor of C57BL/6 mice (H-2b). These tumors cross-react serologically. The effector cells that were generated after the in vitro cultivation recognized tumor-associated antigens on the target cells. H-2 alloantigens were not recognized by the effector cells. The effector cells that killed RBL5 tumor in a genetically nonrestricted manner were identified as T cells. The in vivo carried tumor YAC, in contrast to the in vitro carried tumor YAC-1, could not induce anti-RBL5 reactive cells in A mice. Instead, YAC tumor induced suppressor cells in A mice, which could abrogate the anti-RBL5 cytotoxic response of RBL5-primed splenocytes, but not that of YAC-1 primed splenocytes.     

H-2 effects on cell-cell interactions in the response to single non-H2 alloantigens. IV. Variations in the proliferative response to H-Y and H-3

Individual mice were tested for their proliferation T-cell response to H-Y- and H-3-incompatible stimulator cells in secondary mixed lymphocyte culture. Responders expressing the H-2b haplotype were restricted in their response to stimulators presenting H-Y and H-3 in the context of H-2b. Lymphocytes from individual B10 females proliferated in response to H-Y presented with I-Ab and Db. The ratio of I-Ab/Db-restricted responses varied between individual responders, indicating significant qualitative variation between genetically identical responders. The majority of the proliferative response in all tested mice was restricted to the entire H-2b haplotype suggesting complementation of I-Ab- and Db-region genes in presenting the H-Y antigen. Similar observations were made in the response of individual B10.LP mice to the H-3 antigen. H-3-specific, proliferating T cells were restricted to H-3 antigen presented with KbAb and Db with significant variation between individuals in proliferative response to H-3 plus KbAb and Db. In contrast to the response to H-Y, the proliferative response to H-3 plus H-2b could be accounted for by the summation of the proliferative responses to H-3 plus KbAb and Db. These observations demonstrate that the proliferative response to non-H-2H antigens in the context of I-region determinants is not a sine qua non for the T-cell response to these antigens. Further, the individual qualitative and quantitative variation observed with individual genetically identical mice has strong implications for our knowledge of intrastrain variation in immune responsiveness and the characterization of inbred strains for immune responsiveness.     

Chemotherapeutics and radiation stimulate MHC class I expression through elevated interferon-beta signaling in breast cancer cells

Low doses of anticancer drugs have been shown to enhance antitumor immune response and increase the efficacy of immunotherapy. The molecular basis for such effects remains elusive, although selective depletion of T regulatory cells has been demonstrated. In the current studies, we demonstrate that topotecan (TPT), a topoisomerase I-targeting drug with a well-defined mechanism of action, stimulates major histocompatibility complex class I (MHC I) expression in breast cancer cells through elevated expression/secretion of interferon-β (IFN-β) and activation of type I IFN signaling. First, we show that TPT treatment elevates the expression of both total and cell-surface MHC I in breast cancer cells. Second, conditioned media from TPT-treated breast cancer ZR-75-1 cells induce elevated expression of cell-surface MHC I in drug-naïve recipient cells, suggesting the involvement of cytokines and/or other secreted molecules. Consistently, TPT-treated cells exhibit elevated expression of multiple cytokines such as IFN-β, TNF-α, IL-6 and IL-8. Third, either knocking down the type I interferon receptor subunit 1 (IFNAR1) or addition of neutralizing antibody against IFN-β results in reduced MHC I expression in TPT-treated cells. Together, these results suggest that TPT induces increased IFN-β autocrine/paracrine signaling through type I IFN receptor, resulting in the elevated MHC I expression in tumor cells. Studies have also demonstrated that other chemotherapeutic agents (e.g. etoposide, cisplatin, paclitaxel and vinblastine) similarly induce increased IFN-β secretion and elevated MHC I expression. In addition, conditioned media from γ-irradiated donor cells are shown to induce IFN-β-dependent MHC I expression in unirradiated recipient cells. In the aggregate, our results suggest that many cancer therapeutics induce elevated tumor antigen presentation through MHC I, which could represent a common mechanism for enhanced antitumor immune response through T cell cytotoxicity during metronomic chemotherapy, as well as increased efficacy of combined chemo- (or radio-)/immuno-therapy.