Loss of H-2Kk gene product(s) from an AKR spontaneous leukaemia

Introduction

This chapter focuses on the discovery of the Major Histocompatibility Complex (MHC) in mice (H-2) and in humans (HLA), and on the role played by the International HLA Workshops in the analysis and characterization of this complex genetic system. The early days of Tumour Immunology and the importance of the definition of Tumour Associated Transplantation Antigens (TATA) are also discussed. Today we know that tumour cells can be killed by T lymphocytes by recognizing tumour antigenic peptides presented by MHC molecules and they can also escape this recognition by losing the expression of MHC molecules. This important phenomenon has been profoundly studied for many years both in my lab in Granada and in other laboratories. The results of this research have important implications for the new generation of cancer immunotherapy that boosts T cell responses. A historical perspective of major discoveries is presented in this chapter, with the names of the scientists that have made a significant contribution to the enormous progress made in the field of Tumour Immunology.

MHC class I gene expression and regulation

Major histocompatibility complex (MHC) is a conglomerate of genes that play an important role in recognition of self and nonself. These genes are under tight control. In this review we have discussed the transcription processes regulating MHC gene expression. Various biological or chemical modulators can modulate MHC gene expression. The promoter region of class I genes can be activated through several pathways. Hence, these genes are not typical "domestic" genes. Extensive studies on regulation of MHC class I expression, using transfection techniques and transgenic animal models, have resulted in identification of various cis-acting sequences involved in positive and negative regulation of class I genes. Work is in progress to identify the transacting proteins that bind to these sites and to delineate the mechanisms that regulate constitutive and inducible expression of class I genes in normal and diseased cells. It has been seen that various biological molecules (IFN, GM-CSF, IL-2) and other chemicals up-regulate the MHC expression. If the exact mechanisms are known by which the expression of class I genes is up regulated, the efforts can be made to balance the beneficial and toxic effects of biological molecules with one another, which may facilitate the use of combination of these molecules in subpharmacological doses (to eliminate toxicity) for early and better management of neoplastic diseases, as it is well-known that during malignancy MHC gene expression is down-regulated. In the future, the use of transgenic and knockout mice will be useful in acquiring a better understanding, which may further help in cancer therapy.

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.

Characterization of human amniotic epithelial cells transformed with origin-defective SV40 T-antigen gene

This paper describes characteristics of human amniotic epithelial cells (AEC) transfected with a gene of origin-defective simian virus (SV) 40 large T-antigen (pMTIOD). Normal AEC before transfection with pMTIOD exhibited only low proliferative potential under our culture conditions. On the other hand, AEC cells transfected with pMTIOD exhibited greater proliferative potentials. Flow cytometry and immunohistochemistry analyses showed that both the primary and the transfected AEC did not express appreciable levels of class II antigens. However, the expression of class I antigen of the transfected AEC cells was slightly increased. The cells obtained in this experiment have the ability to induce tumors in severely combined immunodeficiency mice. This finding suggests that established AEC line can be used as a tool to investigate possible expression of the desired gene in human AEC and the gene products, however, was not suitable as a gene carrier to the recipient. Further experiments will be required to establish AEC as a transgene carrier for somatic cell gene therapy.

HLA antigen expression and malignant mesothelioma

The expression of HLA antigens by a tumor may determine its progression and metastatic potential by influencing the immune response to that tumor. The upregulation of HLA antigen expression on some cell types by interferons (IFNs) may contribute to their antitumor activity. Malignant mesothelioma (MM) is a tumor that has a poor prognosis and is unaffected by conventional therapy, although immunotherapy has not been adequately assessed. In this study, we have examined the constitutive and IFN-inducible expression of class I and class II HLA antigens on MM cell lines using indirect immunofluorescence and Northern blotting. All MM cell lines constitutively expressed class I, but not class II, surface antigen, and all three class I loci (HLA-A, HLA-B, and HLA-C) were expressed. The MM cell lines were heterogeneous in their response to the IFNs. Treatment with IFN-alpha marginally increased class I surface expression, but not class II. Class I mRNA was, however, clearly increased in all cell lines after IFN-alpha treatment, suggesting that class I surface antigen was already maximally expressed. IFN-gamma increased class I mRNA expression in all but one cell line and induced DR expression on three of the cell lines. DQ-beta, but not DQ-alpha, mRNA was inducible in the same three cell lines, but DQ surface antigen was never demonstrable.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered expression of HLA-A,B specificities on acute lymphoid and myeloid leukaemia blasts

HLA-A,B specificities were analysed on the neoplastic blasts of a panel of 69 lymphoblastic (ALL) and 50 non lymphoblastic (ANLL) acute leukaemias at onset using the standard lymphocytotoxicity technique. Analysis of the number of detected specificities per locus and, when possible, comparison of the results with those obtained on lymphocytes of the same patients during remission revealed many alterations in the expression of A,B specificities including extra specificities both at the HLA-A and -B loci mainly on lymphoblasts and missed specificities mainly at the HLA-B locus on myeloblasts. Lack of A,B antigens was complete in 6.2% of all tested samples (9% of ANLL) and selective for all the products of one locus in 16.8% of all tested samples (27.7% of ANLL). A decrease of class I molecules on the cell surface was evidenced with MoAb W6/32 on blasts missing detectable serological specificities.

Expression of HLA class I antigens in human tumors and their involvement in tumor growth

A decreased expression of major histocompatibility complex (MHC) class I antigens is a common feature of many experimental and human tumors and can often be correlated with malignancy grade. In fact, reduction of class I antigens is associated in most tumors with an enhanced ability to elude immune surveillance. Loss of HLA-A,B,C antigens ranges from a decrease in the percentage of A,B,C-positive cells to selective loss of particular antigens and total loss of class I molecule expression. In man, this has been documented in melanomas, carcinomas, lymphomas, neuroblastoma and acute leukemias. The reduction in membrane antigens is generally associated with a parallel fall in immunoprecipitable intracellular proteins and the corresponding mRNAs in the absence of structural changes in the coding genes. The literature concerning the above mentioned topics is reviewed and discussed.

Expression of MHC class I and class II antigens in colonic carcinomas

Malignant and non-malignant ('normal') colonic tissues from patients with colonic carcinoma were examined for the expression of MHC class I and class II antigens by immunoenzymatic staining using monoclonal antibodies. The amount of class I antigen as detected by 2 monoclonal antibodies, FMC 16 or W6/32 was clearly diminished in 11 of 14 tumours when compared to the amount present on 'normal' colonic tissue from the same individual. The loss of class I antigen did not correlate with tumour stage or differentiation. The reactivities of FMC 16 and W6/32 with these tissues were not identical, which indicates that the 2 monoclonal antibodies may recognize different epitopes on the HLA class I molecule. Class II antigens were absent from 'normal' colonic epithelium but were present on 20 of 28 tumours, with DR being detected more often than DP, and DQ found only on 4 of 28 tumours. When present, staining for class II antigens was heterogeneous within the tumour, in that all tumour cells did not stain equally. DR and DP antigens were found more often on moderately or poorly differentiated adenocarcinomas and on stage B, C and D tumours in that order of frequency. Thus tumours with a better prognosis were less likely to express DR and DP. The expression of DQ was unrelated to staging or differentiation.

Experimental strategies for modification of histocompatibility antigens in tumor cells

Cancer may be thought of as an immunological disorder that arises because certain 'transformed' cells, endowed with the propensity to divide, have learned to evade detection by the immune system. The prospect of intervention by 'immunotherapy' depends very much on our ability to either [1] render cancer cells more recognizable to the immune system, or [2] potentiate the immune system towards a more effective recognition of cancer cells. There is now direct evidence that suppression of the major histocompatibility complex class I antigens, a family of cell-surface glycoproteins required for the presentation of cancer cells to the immune system, is directly responsible for the ability of tumor cells to escape immune surveillance. It has been shown that cancer cells can be made immunogenic either by the expression of an exogenous class I gene introduced by DNA-mediated gene transfer, or by the derepression of endogenous class I genes with interferon; these cells are efficiently rejected by the immune system. Even more interesting is the finding that the immune system can be potentiated to reject tumors by immunization with homologous tumor cells that have been manipulated to express normal levels of class I antigens. Since increasing numbers of human tumors have been found to have greatly reduced levels of class I antigens, these findings suggest a direct route to immunotherapy that involves debulking of the tumor mass, raising the level of class I antigens in a small number of explanted tumor cells, and re-immunizing the host.

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.

The expression of murine Qa region gene product(s) in L cell transformants

The cosmid H3.5, containing genes mapping to the murine H-2 Qa region, was used to transfect L cells by the calcium phosphate co-precipitation method. The resultant transfected cells expressed a Qa-like determinant as detected by an immune serum raised against the transfectant cells and Qa specific monoclonal antibodies. Two-dimensional gel analysis revealed the expression of a class I-like heavy chain with a similar molecular mass to the Qa2 antigens of the positive strain B10 and B10.A but with a different isoelectric point. The cosmid H3.5 spans 40 kb of DNA and contains at least one complete Qa region gene which encodes the Qa-like determinant detected in this study.

Resistance to cellular immune response in AKR leukemias

Spontaneous AKR leukemias express murine leukemia virus (MuLV) gag and env gene-encoded structural proteins on their cell surface. Cytotoxic T lymphocytes (CTL) induced in AKR mice by syngeneic leukemia 369 which expressed high amounts of H-2 antigens recognized viral gag polyproteins in association with H-2K antigens as target antigens. H-2K-negative leukemias were resistant to lysis by AKR/Gross MuLV-specific CTL and did not induce a cellular immune response. However, they became susceptible after stimulation with interferon. H-2K-positive leukemias induced CTL which were cytotoxic for 369 cells. However, the majority of H-2K-positive leukemias was not lysed by CTL induced by autologous immunization. These leukemias were also resistant to lysis by anti-369 CTL, but could restimulate AKR/Gross-specific CTL in vitro, and were susceptible to lysis by H-2Kk-restricted CTL against AKR minor histocompatibility antigens. Thus, there could be specific defects of the H-2Kk antigens of these tumors. However, there were also qualitative and quantitative differences in antigenic determinants of the gag target antigens in these leukemias. Therefore, in addition to quantitative reduction of the H-2K restriction elements, qualitative alterations of H-2 antigens or of the viral target antigens may impair T cell cytotoxicity and thus influence leukemogenesis of AKR spontaneous leukemia.

Differential expression of HLA class I and II antigens in primary and metastatic melanomas

Class I and II histocompatibility antigen expression was studied in cryostat sections of biopsy tissues from 15 patients diagnosed as suffering from malignant melanoma, using monoclonal antibodies against HLA class I and II monomorphic determinants and an indirect immunofluorescence technique. Class I antigens were detected in three of the four primary melanomas and in five of the eleven metastatic melanomas. Class II antigens were expressed only in metastatic melanomas, in three out of eleven cases. Some tumour cell suspensions were obtained and short-term cultures were established. Radiobinding and immunoprecipitation studies were carried out in two cases, named M6 and M8. The results were comparable to those obtained with direct immunofluorescence. We modulated the expression of class I and II HLA antigens with interferon in M6 when adapted to tissue culture. This melanoma was class I and II negative; after IFN gamma treatment it became strongly positive for class I and II antigens. In addition we have demonstrated, using Southern blot analysis with the restriction enzymes PvuII and EcoRI, that the M6 melanoma does not have any detectable alterations in its class II beta genes.

Immunogenicity of H-2 positive and H-2 negative clones of a mouse tumour, GR9

The GR9 tumour was induced with methylcholanthrene in a BALB/c mouse, adapted to tissue culture and cloned without any passage in vivo GR9 clones were typed for H-2 with three monoclonal antibodies that define H-2Kd + Dd, Kd and Dd antigens. A great heterogeneity of H-2d expression was found from clones which were Kd and Dd positive to clones Kd and Dd negative. These results were confirmed for A7 and B9 clones using immunoprecipitation with anti-H-2D.4 and anti-H-2K.31 alloantisera and SDS-PAGE analysis. In addition, the number of chromosomes per cell was heterogeneous amongst the clones, ranging from 38 +/- 2 to pseudotetraploid clones which have 75 +/- 2 chromosomes. GR9 clones were injected into syngeneic BALB/c mice to measure local tumour growth. We found that the growth correlated with the amount of H-2 antigen expressed, i.e. clones with low H-2d expression were highly malignant while clones with normal H-2d expression were highly immunogenic. Finally we found that BALB/c mice immunized against A7 (Kd, Dd-positive) protected against A7, as expected, but surprisingly also against B9 (Kd, Dd-negative).

Aberrant MHC antigens in a sarcoma virus-induced mouse tumour

From a series of mouse sarcomata, newly induced by Rous sarcoma virus (RSV), the DOH cell line was shown to lack expression of syngeneic H-2Kd and Dk antigens (Noll et al., 1986). It unexpectedly displayed determinants specific for H-2Kk molecules. Interferon treatment of DOH stimulated the expression of H-2Kk determinants and also the display of some, but not all, determinants of the syngeneic H-2Kd molecules. H-2Dk expression was not stimulated. Southern blot hybridization of genomic DNA digests from DOH cells confirmed the identity of the H-2K region with that from syngeneic C3H.OH liver cells, but also showed changes in the pattern of restriction fragments that contain class I genes from the D and Qa regions. These results suggest that aberrant MHC class I molecules that carry H-2Kd- and H-2Kk-like determinants are expressed by DOH sarcoma cells. These molecules may act as target antigens for tumour-specific cytotoxic T cells elicited by injection of DOH cells into syngeneic mice.

Control of synthesis and expression of H-2 heavy chain and beta-2 microglobulin in AKR leukemias

In a series of newly isolated AKR leukemias, some tumors expressed large amounts of both H-2K and H-2D molecules, while others had reduced levels of both antigens. The number of H-2 antigens expressed in steady state showed a consistent correlation with the rate of synthesis of the H-2 class I heavy chain and the beta-2 microglobulin (beta 2m) light chain, and with the amount of H-2- and beta 2m-specific mRNA present in the tumors. Stimulation of leukemic cells with interferon induced an increased transcription of both H-2 and beta 2m mRNA. These results suggest that there is a mechanism that regulates, at the transcriptional level, the coordinate expression of H-2K and H-2D heavy chains, and the beta 2m light chains encoded by genes on chromosomes 17 and 2, respectively.

Abrogation of metastatic properties of tumour cells by de novo expression of H-2K antigens following H-2 gene transfection

H-2 gene transfection was used to restore expression of H-2K antigens in metastatic and non-metastatic subclones of a murine fibrosarcoma that lack their major histocompatibility complex-encoded H-2K antigens. De novo expression of H-2K reduced tumorigenicity and abolished the formation of metastasis in syngeneic mice. Expression of H-2K may lead to effective recognition of the disseminating tumour cells by the host immune system.

The differential expression of H-2K versus H-2D antigens, distinguishing high-metastatic from low-metastatic clones, is correlated with the immunogenic properties of the tumor cells

Two clones of the 3LL Lewis lung carcinoma, a low-metastatic clone A9 and a high-metastatic clone D122, were studied for MHC expression and immunogenic properties. Using monoclonal antibodies, we demonstrated that the A9 clone expresses both the H-2Kb and the H-2Db, whereas the D122 expresses only the H-2Db, and lacks the expression of the H-2Kb encoded molecules. Cells of the low-metastatic clone A9 grew progressively in syngeneic (C57BL/6J) or in F1 mice, but were rejected in allogeneic recipients. The high-metastatic D122 grew progressively in all mouse strains tested, yet metastases were formed only in syngeneic recipients. When H-2 recombinant mice were used, the A9 again manifested a significantly greater immunogenic potency than the metastatic D122, which grew in all 4 recombinants tested. Metastases, however, were formed in B10HTG and to a lesser extent in B10A(4R), thus indicating that metastasis formation is restricted by both C57BL background and H-2Db sub region. We subsequently tested whether the higher immunogenicity of the H-2Kb-positive A9 cells is expressed also in syngeneic mice, to examine whether this could account for its low metastatic phenotype. We found that immunization by A9 cells significantly inhibited the growth of a subsequent A9 graft and even of D122, yet D122 did not retard the growth of secondary D122 or A9 cells. The increased immunogenic effect was expressed also in the generation of syngeneic cytotoxic lymphocytes by A9 but not by D122 cells. We suggest that expression of H-2K molecules on the 3LL clones, immunogenicity and the metastatic phenotype are causally related in this system.

Tumor induction by simian virus 40 in mice is controlled by long-term persistence of the viral genome and the immune response of the host

Simian virus 40 (SV40), which transforms mouse cells in vitro, has not been previously observed to cause tumors when injected in immunocompetent mice. We have investigated both the fate of the injected virion in mice and several immunological parameters as potential factors controlling tumorigenicity. We find that although SV40 does not replicate in mouse cells, the viral DNA can persist for many months postinjection; the majority of the viral DNA is found in the cytoplasm, but a small amount of the viral DNA is integrated at multiple sites in the host nuclear DNA. The persistence of the viral genome is independent of the ability of the mouse to mount an SV40 TSTA specific cytotoxic T-cell response and may be attributed to the cytoplasmic location of the majority of the viral genome. However, in long-term studies of SV40-injected mice, genetically identical except for the major histocompatibility complex, we find that tumors were induced in some mice of the H-2d (low cytotoxic T-lymphocyte responder to SV40 TSTA) but not of the H-2k (high responder to SV40 TSTA) haplotype. Thus, a combination of inefficient disposal of the injected virion and inefficient immunological surveillance and elimination of cells containing nuclear SV40 DNA can eventually result in SV40-induced tumors at multiple sites in mice.

Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

The immunological surveillance hypothesis was formulated prior to the realization of the fact that an individual's effector T cells generally only see neoantigen if it is appropriately presented in the context of self MHC glycoproteins. The biological consequence of this mechanism is that T lymphocytes are focused onto modified cell-surface rather than onto free antigen. The discovery of MHC-restricted T cell recognition, and the realization that T cell-mediated immunity is of prime importance in promoting recovery from infectious processes, has thus changed the whole emphasis of the surveillance argument. Though the immunological surveillance hypothesis generated considerable discussion and many good experiments, there is no point in continuing the debate in the intellectual context that seemed reasonable in 1970. It is now much more sensible to think of "natural surveillance" and "T cell surveillance," without excluding the probability that these two systems have elements in common. We can now see that T cell surveillance probably operates well in some situations, but is quite ineffective in many others. Part of the reason for this may be that the host response selects tumor clones that are modified so as to be no longer recognized by cytotoxic T cells. The possibility that this reflects changes in MHC phenotype has been investigated, and found to be the case, for some experimental tumors. In this regard, it is worth remembering that many "mutations" in MHC genes that completely change the spectrum of T cell recognition are serologically silent. The availability of molecular probes for investigating the status of MHC genes in tumor cells, together with the capacity to develop cloned T cell lines, monoclonal antibodies to putative tumor antigens, and cell lines transfected with genes coding for these molecules, indicates how T cell surveillance may profitably be explored further in both experimental and human situations.

Time course study of H-2 and other antigen expression by hybrids of a myeloma cell line with inflammatory macrophages

The hybrids (the CANS lines) between inflammatory macrophages from C57BL/6N (B6) mice (H-2b) and BALB/c mouse (H-2d)-derived myeloma cell line NS1 in the early period after cell fusion showed no macrophage functions. However, most of the hybrids expressed these functions after prolonged cultivation accompanied with chromosome loss. In contrast, the hybrids initially displaying myeloma functions (kappa light chain production) lost this function when they exhibited macrophage functions. We studied the expression of cell-surface antigens in these hybrids and found that hybrids in the early period after cell fusion codominantly expressed both parental cell H-2 antigens (H-2Kb, H-2Kd, and H-2Dd) but not the H-2Db antigen. On the other hand, aged hybrids strongly expressed the H-2d antigen but lacked the H-2Kb antigen. Alternatively, these aged hybrids with macrophage functions expressed antigen(s) as detected with antiaged CANS-196 cell sera and asialo GM1 antigen, both of which were thought to be found exclusively on macrophages. Thus, the expression of cell-surface antigens in these hybrids was greatly altered after cell fusion.

Impaired H-2 expression in B16 melanoma variants

We studied the expression of H-2b alloantigens in three different B16 melanoma lines cultures in vitro. Cell lines were B16-F1 and two cell cultures (named B16-A and B16-B) newly derived from two different in vivo sublines of B16 melanoma. The assays used were in vivo tumour growth in allogeneic (BALB/c and B10.BR) as compared to syngeneic mice, in vitro cell-mediated cytotoxicity by anti-H-2b immune lymphocytes and absorption of anti-H-2b antisera activity. The B16-F1 line was able to efficiently kill allogeneic hosts, could not be lysed by anti-H-2b cytotoxic effectors and did not express any serologically detectable amount of H-2b alloantigens. The B16-A line was H-2 positive during the early in vitro passages, then, at the 8th-10th passages, it acquired the capacity to kill allogeneic hosts, lost the sensitivity to anti-H-2b cytotoxic effectors and the H-2Kb antigens became undetectable The expression of H-2Db was reduced, although at a lower degree. Similar data were obtained with B16-B cells, which after 10 in vitro passages grew and killed allogeneic hosts, showed a decreased sensitivity to cytotoxic anti-H-2b effectors and a very low expression of the K region antigens. The results indicate that H-2 expression is altered in B16 melanoma lines and this may influence the different metastatic capacity of such cells.

Lack of H-2Ld locus products on a BALB/c fibrosarcoma expressing H-2k-like alien antigens

The presence of H-2Ld antigens was evaluated in methylcholanthrene-induced BALB/c fibrosarcomas by a variety of approaches. Transplantation experiments showed that BALB/c-H-2dm2 mice, a mutant strain whose cells do not express H-2Ld antigens, after immunization with BALB/c normal tissues developed a resistance to the growth of two tumours (C-3 and GI-17), but not to a third neoplasm, C-1, which is known to have H-2d- as well as H-2k-like alien antigens. In vitro experiments with cytotoxic T lymphocytes generated against Ld antigens confirmed a loss of Ld antigens on C-1 but not on C-3 tumour cells. Serological experiments with an anti-Ld serum again revealed the presence of H-2Ld determinants on C-3 but not on C-1 cells. Biochemical analysis in SDS-PAGE of immunoprecipitates obtained by specific anti-H-2 sera with NP40 lysates of the tumours studied could detect H-2Kd, H-2Dd and H-2Ld antigens in C-3 fibrosarcoma cells whereas Kd and Dd were the only H-2d molecules found in C-1 lysate along with the H-2k-like specificities. The possible genetic mechanisms which may explain this apparent gain and loss modification of the H-2 profile of C-1 are discussed.

Dominant allele-specific regulation of expression of H-2Kk gene products revealed by somatic cell hybridization

A study has been made of the H-2 profiles of the AKR thymoma K36 and two series of somatic cell hybrids derived from it. Despite expressing good amounts of the H-2Dk product, the H-2Kk antigen was barely detectable in this tumor, approximately only 1% of that expressed by a comparable AKR lymphoma, 339. The isoelectric focusing profile of the H-2kk product immunoprecipitated from K36 was found to be identical to that from normal AKR lymphocytes. The phenotype of K36 therefore results from regulatory constraints. Fusion of K36 with normal K-2k lymphocytes resulted in hybrids expressing the H-2Kk product. Fusion of K36 with normal H-2b lymphocytes resulted in good expression of the H-2Dk and H-2Db alleles in addition to good expression of the H-2Kb products. The expression of the H-2Kk antigen remained marginal. The data suggest a suppressive mechanism which is trans-acting and dominant and specific for the H-2Kk allele.

Resistance to cell-mediated cytotoxicity is correlated with reduction of H-2K gene products in AKR leukemia

AKR leukemia cell lines differing in the amount of H-2K and H-2D antigens expressed on the cell surface were used to assess cell-mediated immune responses in syngeneic mice against Gross/AKR murine leukemia virus (MuLV)-induced tumors. Leukemic cells with reduced expression of H-2Kk antigens were inactive as inducers of Gross-MuLV/H-2k-specific cytotoxic T lymphocytes (CTL) and resistant to lysis by CTL raised against H-2Kk positive AKR leukemia cells. H-2Kk positive leukemias induced cytotoxic effectors, which upon restimulation in vitro, lysed the stimulating and other H-2Kk positive leukemia cells. In antibody inhibition experiments, T-cell-mediated cytotoxicity to these leukemias could only be inhibited by antisera and monoclonal antibodies specific for the H-2Kk antigens. Due to this specific role of H-2Kk antigens in T-cell cytotoxicity to Gross/AKR MuLV-induced tumors, reduced expression of H-2Kk antigens on spontaneous AKR leukemic cells could have important implications for surveillance of these neoplastic cells.

Variation of expression of histocompatibility antigens on tumor cells: absence of H-2Kk-gene products from a gross-virus-induced leukemia in BALB.K

The antigenic profile of the K-GV tumor of BALB.K origin, induced by Gross virus and maintained in vitro and in vivo, was investigated by serological and immunochemical methods and techniques of cell-mediated immunity. The H-2Kk-gene products were absent by several criteria: (1) monoclonal antibody and conventional alloantisera directed against eh H-2Kk antigenic specificities were nonreactive by direct testing and by absorptions. (2) H-2Kk products could not be precipitated from glycoprotein or protein extracts of the radiolabeled K-GV tumor. (3) Cytotoxic effectors against H-2Kk produced by sensitization in vitro and in vivo failed to kill K-GV target cells. (4) The tumor could neither stimulate BALB.B congenic mice to produce cytotoxic effectors nor specific cytotoxic antibody against H-2Kk-gene products. In contrast, the H-2Dk antigen was readily detectable by all these criteria. These findings therefore describe a tumor which has selectively lost the H-2K-gene products. The K-GV tumor was able to generate Gross-virus specific CTL, but had greatly reduced susceptibility to lysis by Gross-virus specific CTL generated by H-2K expressing AKR (H-2k) tumors. These findings have important implications for the associative recognition of tumor antigens and the immune surveillance of virally induced tumors.

A miniaturised single-step method of cell cloning

This paper describes a miniaturised method of cell cloning in Terasaki plates. It is rapid and technically simple enabling large numbers of putative clones to be tested. As Terasaki plates are designed for use in tissue typing procedures, the wells can be screened and the exact number of cells in any particular well can be seen. Colonies derived from wells containing only one cell can then be chosen, eliminating the need for a second or third recloning usually necessary for statistical surety.

Interspecies exchange of beta 2-microglobulin and associated MHC and differentiation antigens

Radiolabeled human beta 2-microglobulin (beta 2m) can bind to mouse histocompatibility (H-2) antigens on the cell surface or to partially purified H-2 antigens in solution. The complexes containing human beta 2m and H-2 antigens from C3H (H-2k) mice could be immunoprecipitated specifically with alloantisera, rabbit anti-H-2 xenoantisera, and with monoclonal H-2-specific antibodies. Specific association with H-2 antigens was also observed with other haplotypes. The only exception was B10.D2 (H-2d) from which complexes containing human beta 2m could only be precipitated with anti-H-2-xenosera. Thus radiolabeled human beta 2m can be used as a specific label for mouse H-2 antigens in precipitation and radioimmunoassays. The application of this finding extends to major histocompatibility complex antigens of other species, and to differentiation antigens with primary association with beta 2m.

Serological detection of H-2K- and H-2D-gene products. I. Principal difference between T and B lymphocytes in expression of H-2D-encoded alloantigens

Using the fluorescence-activated cell sorter (FACS II), we have analyzed the expression of H-2K- and H-2D-gene products on the membrane of various cellular components of the murine immune system. Using this serological technique we show a basic difference between T and B lymphocytes. Whereas all cellular components analyzed--hydrocortisone-resistant thymocytes, splenic T and B lymphocytes, macrophages and bone-marrow cells--expressed H-2K-subregion-encoded alloantigens at a high density, it seems that the high density expression of H-2D-encoded alloantigens is restricted mainly to B cells and to macrophages. Hydrocortisone-resistant thymocytes, splenic T lymphocytes and bone-marrow cells, on the other hand, showed significant expression of the H-2D alloantigens only at low membrane density. These results, then, provide evidence for the existence of an imbalance in serologically detectable expression of H-2K- and H-2D-region-gene products on the cell membrane of various cells comprising the murine immune system.

Differential expression of H-2 gene products in tumour cells in associated with their metastatogenic properties

Many neoplasms seem to be heterogeneous in nature, producing metastases by pre-existing variant cells with inherent biochemical and biological properties. The survival and proliferation of metastatic cells depend on various biological properties, such as enzymes which degrade basement membranes, resistance to various host defence systems, association with host cellular components, adhesiveness and expression of certain membrane glycoproteins. Recent studies have indicated that metastatic cells may differ from the local tumour cells in the expression of immune recognizable membrane-associated antigens. Such antigenic differences may result from an immunoselection of cells with distinct antigenic properties due to a specific immune response evoked against the local tumour. In view of the role of the major histocompatibility complex (MHC) system in controlling and restricting the function of immune effector cells against modified self-components, one could assume that the modulation of the expression of MHC-encoded antigens on the membrane of tumour cells influenced the interclonal relationship within a local heterogeneous tumour cell population and the subsequent generation of metastasis. The modulation of the expression of H-2 antigens on several murine tumours is well documented; however, practically no attempts were made to relate H-2 modulation with invasiveness. We now describe principal differences in the expression of H-2 parental haplotypes between a local F1 methylcholanthrene-induced tumour and its descendant pulmonary metastases. These results suggest that both the expression and the immunogenicity of MHC products strongly influence the immune relationship between the tumour and the host's immune system, thus determining the generation and dissemination of metastases.

Establishment and characterization of cell lines from homozygous brachyury (T/T) embryos of the mouse

Lethal mutations in the T/t complex cause stage-specific morphologic abnormalities during early embryogenesis of mice. Although mutant embryos are lethal at the early stages of development, we have succeeded in establishing several cell lines from one of these mutants (T/T). Mutant-specific abnormality was not observed in gross morphology and growth patterns of cells. They, however, retained the characters of freshly dissociated embryonic cells to form smaller aggregates than the wild-type in rotation-mediated aggregation. One of the T/T cell lines (T-1) formed tumors when injected into one-day-old syngeneic and allogeneic host. Expression of H-2 antigens was serologically studied with H-2 specificity 5 as a marker antigen. All lines except T-1 were shown to have this specificity.

Serological and immunochemical studies of H-2 allospecificities on K36, a syngeneic tumour of AKR

Expression of H-2 antigenic specificities on K36, a spontaneous leukaemia originating from AKR (H-2k) mice, was studied by serology and immunochemistry. Two ascites lines of the tumour, as well as a tissue culture adjusted and cloned tumour line, were used in these studies with similar results being obtained. K36 expresses on its cell surface D-region encoded H-2K antigens but does not express K-region encoded H-2K alloantigens. It also expresses on its cell membrane, H-2 specificities of foreign haplotypes not present on normal AKR lymphoid cells. The molecular basis of the H-2Dd specificity on K36 (H-2k) was analysed by immunoprecipitation and polyacrylamide gel electrophoresis. The specificity was shown to be present on a glycoprotein of apparent molecular weight 45,000. However, antisera against the H-2Dd private specificity (H-2.4) precipitate additional glycoprotein of 45,000D and also 70,000D. In tryptic peptide maps of the isolated 45,000D fraction precipitated by anti-H-2.4 serum from radiolabelled K36 glycoprotein, all H-2Dd specific peptides were present in the same quantitative ratio. This is consistent with the structural identity of the foreign H-2Dd from the K36 tumour with normal H-2Dd and supports the hypothesis of a regulator system controlling the H-2 allelism. Under certain circumstances such a system could cause suppression of one and derepression of the other H-2 gene products.