Differential induction of H-2K versus H-2D class I major histocompatibility antigens by recombinant gamma interferon. Lack of Kk augmentation in a leukemia virus-induced tumor is due to a cis-dominant effect

MHC heterogeneity and response of metastases to immunotherapy

In recent years, immunotherapy has proven to be an effective treatment against cancer. Cytotoxic T lymphocytes perform an important role in this anti-tumor immune response, recognizing cancer cells as foreign, through the presentation of tumor antigens by MHC class I molecules. However, tumors and metastases develop escape mechanisms for evading this immunosurveillance and may lose the expression of these polymorphic molecules to become invisible to cytotoxic T lymphocytes. In other situations, they may maintain MHC class I expression and promote immunosuppression of cytotoxic T lymphocytes. Therefore, the analysis of the expression of MHC class I molecules in tumors and metastases is important to elucidate these escape mechanisms. Moreover, it is necessary to determine the molecular mechanisms involved in these alterations to reverse them and recover the expression of MHC class I molecules on tumor cells. This review discusses the role and regulation of MHC class I expression in tumor progression. We focus on altered MHC class I phenotypes present in tumors and metastases, as well as the molecular mechanisms responsible for MHC-I alterations, emphasizing the mechanisms of recovery of the MHC class I molecules expression on cancer cells. The individualized study of the HLA class I phenotype of the tumor and the metastases of each patient will allow choosing the most appropriate immunotherapy treatment based on a personalized medicine.

Cytotoxic T lymphocytes to endogenous mouse retroviruses and mechanisms of retroviral escape

Mouse retrovirus-induced lymphoma/leukemia and immunodeficiency are useful models for analogous human diseases. Both ecotropic (mouse tropic) and recombinant retroviruses, including the polytropic mink cytopathic focus-inducing type, have been studied for disease pathogenesis and as targets for humoral and cellular immunity, particularly cytotoxic T-lymphocyte (CTL) responses. For AKR/Gross murine leukemia viruses (MuLV) we have defined an immunodominant CTL epitope in the p 15E transmembrane anchor envelope protein and three minor/subdominant epitopes. Evidence is presented for retroviral escape from CTL by selection following genetic recombination and point mutation both within and outside CTL epitope sequences, and via endogenous retrovirus-infected cell downregulation of the generation of anti-AKR/Gross MuLV CTL. As demonstrated in vivo in naturally occurring non-responder strains by adoptive transfer, and in vitro by cell-mixing experiments, a central non-responsiveness mechanism appears to be peripheral inhibition mediated by infected cells expressing MHC-presented viral peptides. Such inhibition requires Fas expression by antiviral T cells; occurs upon TCR-mediated recognition of virus-infected, Fas ligand-expressing "veto" cells; and apparently leads to an antigen-specific form of activation-induced cell death of T cells. In the LP-BM5 MuLV isolate that causes murine AIDS (MAIDS) retroviral variation also leads to CTL escape--the BM5-helper virus has altered forms of the immunodominant and two minor/subdominant epitopes. In contrast, a novel immunodominant CTL epitope is recognized by MAIDS resistant, but not MAIDS-susceptible, strains. This epitope is uniquely encoded in an alternative translational reading frame of the viral gag gene. It also appears that the LP-BM5 MuLV have co-opted the cells of the immune system for retroviral pathogenesis--CD40/CD40L (CD154) interactions are required both for the initiation and progression of MAIDS.

Interferon-alpha/beta, pentoxifylline, and caffeine synergize with interferon-gamma to induce major histocompatibility complex class I expression on a constitutively class I-negative murine tumor cell line

The constitutively class I-negative tumor cell line, Kgv, expresses H-2Dk in response to interferon-gamma (IFN-gamma), but not in response to IFN-alpha/beta, tumor necrosis factor, or lymphotoxin. H-2Dk expression was not induced on Kgv cells by the methylxanthines, pentoxifylline (PTX) and caffeine, which modulate class I expression on cells that constitutively express class I molecules. Treatment of Kgv cells with either IFN-alpha/beta, PTX, caffeine, or dibutyryl cAMP and a concentration of IFN-gamma insufficient by itself to induce Dk expression resulted in the induction of Dk expression. Since PTX and caffeine are cAMP-specific phosphodiesterase inhibitors, it is possible that the effects of PTX, caffeine, and dibutyryl cAMP involve a cAMP-dependent mechanism. We conclude that concentrations of IFN-gamma insufficient to induce Dk expression on Kgv cells may be capable of rendering the Dk gene responsive to signals that, in the absence of IFN-gamma treatment, have no effect on Dk expression.

Introduction of the H-2Dk gene into a class I-negative tumor cell line confers interferon-gamma inducibility upon the silent endogenous H-2Kk gene

Kgv cells do not constitutively express class I mRNA or protein. Interferon (IFN)-gamma, but not IFN-alpha/beta, induces H-2Dk expression. IFN does not induce H-2Kk expression. We examined constitutive and IFN-inducible class I expression on Kgv cells stably transfected with genomic clones of H-2Kk or H-2Dk and on somatic cell hybrid lines constructed between Kgv cells and constitutively class I-positive cells of a distinguishable H-2 haplotype. Our results suggest that both the lack of constitutive class I expression and the inability of IFN-alpha/beta to induce class I expression on Kgv cells are primarily due to cis-regulatory mechanisms. However, stable introduction of the H-2Dk gene into Kgv cells conferred IFN-gamma inducibility upon the silent endogenous H-2Kk gene. Therefore, the failure of IFN-gamma to induce H-2Kk expression on Kgv cells is due, at least in part, to a trans-regulatory mechanism.

Major histocompatibility complex antigens in v-Ki-ras transformed cells: the different antigens are expressed and induced by interferons independently of one another and of the anti-viral state

A series of cell lines, which differed in their expression of class I (H-2K) or II (I-A) major histocompatibility complex (MHC) antigens, was derived from a line of C3H/He (H-2k) mouse embryo fibroblasts transformed by the v-Ki-ras oncogene. These were prepared by fluorescence-activated cell sorting of cells stained for these antigens either without interferon (IFN) treatment or after induction of antigen expression by either IFN-alpha beta or IFN-gamma, selecting for low or high staining. Cells selected for low (undetectable) constitutive H-2Kk expression were still strongly inducible by either IFN; cells selected for high constitutive expression were induced by IFN to express still higher levels. In all cell lines induction of H-2Kk with one IFN type was paralleled by induction with the other. Expression of H-2Kk appeared largely independent of H-2Dk; in lines which were selected for low H-2Kk expression (constitutive or induced), H-2Dk expression was not much reduced, and lines selected for high H-2Kk expression showed only modest augmentation of H-2Dk. Varying inducibility of I-Ak by IFN-gamma was not closely paralleled by H-2K inducibility by either IFN-alpha beta or -gamma, with again only weak correlation of high and low expression of H2-Kk and I-Ak. On the other hand, expression of I-Ak seemed to be correlated with I-Ek. None of these variable effects could be attributed to differing sensitivity to IFN-alpha beta or -gamma since all the lines showed about the same sensitivity to the anti-viral effects of IFN.

Differential up-regulation of H-2D versus H-2K class I major histocompatibility expression by interferon-gamma: evidence against a trans-acting allele-specific factor

Previous investigation described a unique differential phenotype for the murine T-cell tumor AKR SL3 with regard to augmentation of class I major histocompatibility complex antigen expression by interferon-gamma (IFN-gamma). Dk expression was increased by IFN-gamma as expected, but Kk expression remained at constitutive levels, despite treatment with a range of doses and times of exposure to IFN-gamma. Analysis of somatic cell hybrids obtained by fusion of AKR SL3 with an H-2Kb and Db IFN-gamma augmentable partner tumor argued against the involvement of locus-specific, trans-acting factors as the basis for the nonaugmentable nature of the Kk gene in AKR SL3. Here, we provide evidence against the remaining possibility of an allele-specific, negative-acting factor in AKR SL3. Hybrids were constructed between drug-marked sublines of AKR SL3 and the R1.G1 T-cell tumor which carries IFN-gamma augmentable Kk and Dk genes. The uniform ability of IFN-gamma to cause substantial increases in the expression of Kk in hybrid populations and a large number of hybrid clones from three separate fusions indicated that a trans-acting, negative factor was not present in AKR SL3. Rather, these data coupled with Northern analysis were consistent with cis alterations operating at the level of transcription as the basis for Kk nonaugmentation. These results are discussed with regard to the further study of AKR SL3 to better understand IFN-gamma regulation of class I MHC expression.

Cancer immunology: highlights of the NCI Extramural Immunology Program

The long-term goal of research supported by the Immunology Program is to better understand immune mechanisms and their regulation in order to develop more effective strategies to strengthen the immune response against cancer. While there has been much progress in the field of immunology in recent years, many major questions remain unanswered. The role of MHC antigens in regulating the immune response to tumors is still unclear, as is the nature of putative tumor-associated antigens which are the targets of this response. The efficacy of various immune cell subsets in tumor cell killing is differentially affected by changes in tumor cell surface MHC antigen expression. Furthermore, although we now know much more about the cellular interactions in the immune response, little is actually known about the particular cell subsets which participate in an immune response is regressing versus progressing tumors. Interleukins have been shown to stimulate a variety of immunes response, and some of these immune modulators are now being tested in clinical trials, in various stages, to determine their antitumor effects. However, systemic administration of large quantities of interleukins can result in very different effects than those created by the local release of effector molecules from specific T-cell populations. Effector T cells can deliver lymphokines to precise target structures, whereas systemically administered lymphokines would affect preferentially those cells expressing the largest numbers of high affinity receptors for the lymphokines. The specificity of lymphokines as mediators of immunologic response rests largely or exclusively in the local release of such materials by T cells upon activation by antigen: MHC complexes on a stimulating cell. Because lymphokines show specificity only for nonantigen-specific, non-MHC-restricted receptor molecules on target cells, the effect of lymphokine injections is likely to be determined solely by the expression of these receptors. Thus, lymphokines function well as effector molecules in a number of specific immune reactions, but it remains to be determined whether they will be useful in regulating immune responses in specific disease situations. It may be critical to recruit specific immune cells to the area of tumor growth where they, in turn, can release lymphokines to activate appropriate antitumor effector cells. Adoptively transferred T cells of the helper phenotype can induce an effective antitumor immune response in recipient mice.(ABSTRACT TRUNCATED AT 400 WORDS)

MHC antigen induction by interferon gamma on cultured mouse pancreatic beta cells and macrophages. Genetic analysis of strain differences and discovery of an "occult" class I-like antigen in NOD/Lt mice

This study provides a basis for understanding the wide variations reported in the literature in IFN-gamma inducibility of class II MHC antigens on murine beta cells. Inducibility is not an intrinsic property of all mouse beta cells, but instead depends upon strain- (and tissue-) specific response modifying factors. This was demonstrated by comparison of constitutive and IFN-gamma-induced class I and class II MHC gene products on cultured islet cell monolayers. Islet cultures were established from autoimmune diabetes-prone NOD/Lt mice, diabetes-resistant NON/Lt and CBA/J mice, as well as F1 hybrids between these latter two strains and NOD/Lt. Cultures of peritoneal macrophages (M phi) from each strain were established as controls. After 3 wk of culture (with incubation in the presence or absence of IFN-gamma during the last 6 d), constitutive expression as well as IFN-gamma induction of class I MHC antigen expression was demonstrated on NOD/Lt and NON/Lt islet cells by antibody plus complement-mediated cytotoxicity. Although CBA/J islets and M phi did not maintain constitutive class I or class II antigen expression in culture in the absence of IFN-gamma, class I H-2Kk antigen was IFN-gamma inducible. Whereas IFN-gamma-induced class II I-Ak antigen on CBA/J M phi, it failed to induce this antigen on CBA/J islets. In contrast, I-A antigens were IFN-gamma inducible on NOD/Lt and NON/Lt islets and M phi. In (CBA x NOD)F1 hybrids, loss of IFN-gamma inducibility of the I-ANOD product established that suppression was mediated by a trans-acting factor from the CBA/J genome. In the course of these studies, IFN-gamma inducibility of a crossreactive occult class I-like antigen on both NOD/Lt islet cell and M phi cultures was unexpectedly detected when mAb 28-13-3 (public specificity 39, reactive with H-2Kb,f) was used as a negative control. Although not detectable by cytofluorographic analysis of freshly isolated NOD/Lt splenic leukocytes, occult antigen could be induced on NOD/Lt peritoneal macrophages (M phi) cultured for 3 d in IFN-gamma. Time course of induction showed the occult antigen to be distinct from NOD/Lt class I and II gene products. In both islet cell and M phi cultures established from (CBA x NOD)F1 hybrids, trans-suppressive factor(s) from the CBA/J genome not only suppressed IFN-gamma-induced expression of I-ANOD, but additionally suppressed occult antigen induction. Backcross of F1 to both parental strains indicated that the occult locus was on Chr 17, tightly linked to MHC.(ABSTRACT TRUNCATED AT 400 WORDS)

Cis-acting elements determine the locus-specific shutoff of class I major histocompatibility genes in murine S49 lymphoma sublines

Several tumors have been reported to down-regulate expression of their class I major histocompatibility molecules, potentially altering their immune recognition. To investigate this phenomenon, we are using various sublines isolated from the S49 lymphoma of the BALB/c mouse strain. These S49 tumor sublines were previously found to have shut off expression of their Kd, Dd, and/or Ld class I molecules in a locus-specific manner. Extensive Southern blot analyses indicated that there were no major chromosome aberrancies in these S49 sublines, and analyses of steady-state class I mRNA suggested that a form of transcriptional regulation was responsible for their variant class I expression. In this report, we characterize the nature of this locus-specific regulation of class I in S49 cells by producing somatic cell hybrids. Three phenotypically distinct S49 sublines were each fused to tumor cells with normal class I expression, and several of the resulting hybrids were analyzed. In every case, the class I molecules expressed by the hybrids were an exact composite of the two fusion partners. Thus, these fusions failed to rescue expression of the Kd, Dd, and/or Ld molecules shut off within each of the S49 tumor sublines. These findings indicate that this locus-specific shutoff of class I expression results from a cis-acting defect and not trans-acting factors. Because the analysis of each of three phenotypically different S49 cells implicated a form of cis-dominant regulation, we hypothesize that a common mechanism generating homologous mutations in class I genes is operative in S49 tumor cells.