Suppressor cell clones specific for ultraviolet radiation-induced tumors. Function and surface proteins

Lymphocytes were cloned from animals bearing UV-induced skin tumors. These cells were I-J+, CD4-, CD8-, and had become growth factor independent. Extracts, but not supernatants, of these clones suppressed primary immune reactions in vitro against UV-induced tumors, but not methylcholanthrene-induced tumors. The cells therefore had the functional characteristics of afferent suppressor T cells directed against a common Ag on UV-induced tumors. Surface iodination of the clones revealed an extremely low level expression of molecules that might be TCR or related molecules.     

Identification of IL-7-dependent bone marrow-derived Thy-1-B220- lymphoid cell clones that rearrange and express both Ig and T cell receptor genes.

Bone marrow stromal cell lines and lymphoid cell lines were co-established from the Whitlock-Witte type of long term liquid cultures of MRL/1 and C57BL/10 (B10) (Thy-1.1) bone marrow cells. The present study investigates the immunologic nature of parental and cloned lymphoid cell lines. Both strains of parental lines and their clones did not grow alone but proliferated on the monolayers of co-established parental stromal cell lines from a syngeneic or alternative strain. When various lymphokines or cytokines were tested for their capacity to support the growth of these lymphoid cell clones, only IL-7 could substitute for the growth-promoting function of stromal cells. These IL-7-dependent clones expressed neither Thy-1 nor B220 Ag. However, all of them from two strains were found to rearrange synchronously H chain of Ig as well as gamma chain of TCR genes. Some of the clones transcribed a mature size of IgH mRNA. Co-expression of mRNA for lambda 5 but not for IgL chain (kappa, lambda) genes resulted in the generation of cell surface mu chain in these clones. Other clones expressed a smaller size of IgH mRNA without exhibiting surface mu chain. Irrespective of the differences in IgH rearrangements and its mRNA expression, a mature size TCR gamma mRNA was detected in all of the clones. Thus, these results demonstrate the existence of untransformed (IL-7-dependent) immature lymphoid cells rearranging both Ig and TCR genes. Their unique features concerning cell surface markers (B220- mu+), specific growth factor requirement, and various modes of Ig/TCR gene rearrangements are discussed in the context of early lymphoid development.     

CD3- T cells with cis- or trans-acting mutations affecting expression of T cell receptor beta-chain mRNA.

Mutants of an untransformed T cell clone that no longer respond to TCR/CD3 stimulation have been derived using a selection procedure based on the loss of functional response to Ag. This functional selection gives rise to clones of several different phenotypes. We have previously described mutants with a TCR/CD3+ cell surface phenotype whose TCR are uncoupled from cellular responses. We describe six additional mutants that do not express TCR/CD3 at the cell surface. One of the CD3- clones contains a deletion in the successfully rearranged TCR-alpha gene, whereas another carries a deletion in the successfully rearranged TCR-beta gene. TCR/CD3 expression in these deletion mutants can be restored by transfection of TCR-alpha or TCR-beta DNA. Four other clones do not express TCR-beta mRNA, yet contain no obvious deletions or rearrangements in the TCR-beta genes. One of these clones does not transcribe TCR-beta chain mRNA. The mutation in this clone does not reside in the TCR-beta gene itself, but may instead reside in a trans-acting regulatory element affecting TCR-beta gene expression, because the TCR-beta mRNA-phenotype is complemented by fusion with a TCR-alpha-beta- cell line. TCR-beta chain regulatory mutants will be valuable in contributing to our understanding of how TCR expression is regulated.     

Most IL-4-producing gamma delta thymocytes of adult mice originate from fetal precursors

Thy-1(dull) gammadelta T cells constitute a distinct adult gammadelta T cell subset characterized by the expression of a TCR composed of Vgamma1Cgamma4 and Vdelta6Cdelta chains with limited junctional sequence diversity. However, several features of the expressed Thy-1(dull) TCR-gammadelta genes, in particular the absence or minimal presence of N region diversity and the almost invariable Ddelta2-Jdelta1 junction, are typical of rearrangements often found in the fetal thymus. In this study, we have investigated the origin of these cells. Few Thy-1(dull) gammadelta thymocytes developed in syngeneic radiation adult chimeras, regardless of whether the recipient mice were given adult bone marrow or fetal liver cells as a source of hemopoietic precursors. In contrast, normal numbers of Thy-1(dull) gammadelta T cells developed in fetal thymi grafted into adult syngeneic recipients. Interestingly, the majority of Thy-1(dull) gammadelta thymocytes present in the grafts were of graft origin, even when most conventional gammadelta and alphabeta thymocytes in the grafted thymi originated from T cell precursors of recipient origin. Single-cell PCR analyses of the nonselected TCR-gamma rearrangements present in adult Thy-1(dull) gammadelta thymocytes revealed that more than one-half of these cells represent the progenies of a limited number of clones that greatly expanded possibly during the first weeks of life. Finally, the second TCR-delta allele of a large number of Thy-1(dull) gammadelta T cells contained incomplete TCR-delta rearrangements, thus providing an explanation for the adult-type rearrangements previously found among nonfunctional V(D)J rearrangements present in Thy-1(dull) gammadelta thymocytes.     

Patterns of T cell receptor gamma gene rearrangements in human CD3+ clones derived from WT31- or Leu7+ cells in relation to non-MHC-restricted cytotoxic activity

Clones were obtained from human peripheral blood WT31-, WT31-CD4-8-, CD4-8- or Leu 7+ cells in the presence of interleukin 2 and phytohaemagglutinin. Almost all clones were CD3+, about 50% were CD4-8- and all clones tested derived from WT31- remained WT31-, indicating that they were expressing a gamma/delta heterodimer in association with CD3. Some clones derived from CD4-8- cells expressing CD3 were WT31- and some were WT31+. All CD3+ clones had T cell receptor (TCR) gamma gene rearrangements; most also had their TCR beta genes rearranged, including all clones derived from Leu 7+ cells. TCR gamma gene rearrangements were noted involving all five known J segments. There was a tendency for V gene segments from the VII and VIII subgroups to be rearranged to J gamma 2 less often than those from the more 5' VI subgroup. Two clones definitely had one rearrangement to C gamma 1 and one to C gamma 2. When clones derived from WT31- cells were considered, the only obvious relationship which emerged was that all clones with both chromosomes rearranged to C gamma 2 had low or negligible cytotoxic activity against natural killer (NK)-sensitive and NK-resistant targets. Several of these clones were expressing CD8 on about 30% of cells. Most clones with rearrangements involving only C gamma 1 had high non-MHC-restricted cytotoxicity while those with at least one C gamma 1 rearrangement had either high or low activity. The only exceptions noted were a clone with a single V9JP rearrangement and a clone with a V9JP and a VI/IIIJP1 rearrangement, which both had low activity. A similar pattern was also found with most clones derived from Leu 7+ cells. The data are consistent with the participation of most types of disulphide-linked (C gamma 1) gamma/delta heterodimers in non-MHC-restricted cytotoxic activity mediated by CD3+ gamma/delta + T cell clones.     

The CD3-gamma and CD3-delta subunits of the T cell antigen receptor can be expressed within distinct functional TCR/CD3 complexes.

The T cell receptor for antigen (TCR) consists of two glycoproteins containing variable regions (TCR-alpha/beta or TCR-gamma/delta) which are expressed on the cell surface in association with at least four invariant proteins (CD3-gamma, -delta, -epsilon and -zeta). CD3-gamma and CD3-delta chains are highly homologous, especially in the cytoplasmic domain. The similarity observed in their genomic organization and their proximity in the chromosome indicate that both genes arose from duplication of a single gene. Here, we provide several lines of evidence which indicate that in human and murine T cells which expressed both the CD3-gamma and CD3-delta chains on their surface, the TCR/CD3 complex consisted of a mixture of alpha beta gamma epsilon zeta and alpha beta delta epsilon zeta complexes rather than a single alpha beta gamma delta epsilon zeta complex. First, a CD3-gamma specific antibody failed to co-immunoprecipitate CD3-delta and conversely, several CD3-delta specific antibodies did not coprecipitate CD3-gamma. Secondly, analysis of a panel of human and murine T cell lines demonstrated that CD3-gamma and CD3-delta were expressed at highly variable ratios on their surface. This suggested that these chains were not expressed as a single complex. Thirdly, CD3-gamma and CD3-delta competed for binding to CD3-epsilon in transfected COS cells, suggesting that CD3-gamma and CD3-delta formed mutually exclusive complexes. The existence of these two forms of TCR/CD3 complexes could have important implications in the understanding of T cell receptor function and its role in T cell development.     

The joining of germ-line V alpha to J alpha genes replaces the preexisting V alpha-J alpha complexes in a T cell receptor alpha, beta positive T cell line

To determine whether T cell receptor genes follow the same principle of allelic exclusion as B lymphocytes, we have analyzed the rearrangements and expression of TCR alpha and beta genes in the progeny of the CD3+, CD4-/CD8- M14T line. Here, we show that this line can undergo secondary rearrangements that replace the pre-existing V alpha-J alpha rearrangements by joining an upstream V alpha gene to a downstream J alpha segment. Both the productively and nonproductively rearranged alleles in the M14T line can undergo secondary rearrangements while its TCR beta genes are stable. These secondary recombinations are usually productive, and new forms of TCR alpha polypeptides are expressed in these cells in association with the original C beta chain. Developmental control of this V alpha-J alpha replacement phenomenon could play a pivotal role in the thymic selection of the T cell repertoire.     

Inverse correlation between steady-state RNA and cell surface T cell receptor levels.

The relationship between steady-state RNA and cell surface levels of T cell receptor (TCR) was examined in mature T cells and immature CD4+CD8+ double positive thymocytes. TCR is expressed at high levels on the surface of mature T cells and at much lower levels on double positive thymocytes. We demonstrate that in direct contrast to surface expression, TCR-alpha, -beta, CD3-delta, -epsilon, -gamma, and sigma RNA levels are much higher in the immature double positive thymocyte population than in mature T cells. These results demonstrate that quantitative differences in TCR surface expression in immature and mature T cells are not due to increases in TCR RNA levels.     

B lymphoblastoid cell lines with rearranged T cell receptor beta-chain genes retain conventional B cell surface antigen and Ig expression

Transformation of peripheral blood lymphocytes by co-incubation with EBV produces B lymphoblastoid cell lines, but rearrangement of TCR beta-chain genes was observed in three different cell lines derived from two individuals. Because rearrangement of TCR genes in B lymphocytes is considered a rare event, these B lymphoblastoid cell lines with rearranged TCR beta-genes were examined in detail to determine whether there were any additional characteristics to distinguish them from B lymphoblastoid cell lines with germ-line TCR beta-genes. All B lymphoblastoid cell lines contained rearranged Ig H and kappa L chain genes, secreted Ig, and expressed B and not T cell surface markers. Cell lines with rearranged TCR beta-genes had rearranged both IgH genes and had rearranged and subsequently deleted both kappa C region genes. Furthermore all three B lymphoblastoid cell lines with rearranged TCR beta-genes produced small amounts of Ig with lambda-L chains. Although the cellular mechanisms maintaining lineage-specific rearrangement events remain unknown, extensive Ig gene rearrangement and inefficient Ig production by B cells may be indicators of a cellular status where normally stringent lineage-specific control elements fail to function efficiently.     

A T cell clone expresses two T cell receptor alpha genes but uses one alpha beta heterodimer for allorecognition and self MHC-restricted antigen recognition

All of the T cell receptor alpha- and beta-chain rearrangements present in a dual reactive T cell clone were characterized. This clone exhibits allelic exclusion of its beta-chain genes in that only one of the two alleles is productively rearranged. Unexpectedly, it displays two productive V alpha-gene rearrangements, which are both transcribed into 1.5 kb mRNA. The contribution of each of the two productive alpha genes to the dual recognition was analyzed by gene transfer. To this end, each of the two alpha genes was separately transfected with the single productively rearranged beta gene. Transfer of only one of the two alpha beta combinations restored both allogeneic MHC recognition and self MHC-restricted antigen recognition. Thus, T cell dual recognition results from the cross-reactive recognition of an allo-MHC product by a single antigen-specific and MHC-restricted alpha beta T cell receptor. Furthermore, the presence of two productively rearranged alpha-chain genes in a T cell clone raises questions concerning the level at which allelic exclusion operates in T cells.     

Characterization of T cell clones from an athymic mouse.

Although Thy-1+ lymphocytes have been observed in lymphoid tissues of athymic mice, attempts to analyze these cells on the clonal level have previously yielded only populations of CD4-CD8+ cytolytic T cells. Furthermore, studies of responses of these cells to various mitogenic stimuli have demonstrated significant defects in the ability of these cells to proliferate in culture. We report here on the cloning and maintenance in long term culture of T cells from an athymic mouse stimulated in vitro with allogeneic spleen cells. Of 10 Thy-1+ clones, 7 CD4+CD8- and 3 CD4-CD8+ Ag-specific cells were obtained. Among the CD4+ T cells, we observed a variety of specificities, including an autoreactive I-Aq specific clone, a minor lymphocyte stimulating determinant (Mls)-reactive clone, and five allo-I-Ad-specific CD4+ clones; a class II-specific CD4-CD8+ clone was also obtained. In addition, we observed two Thy-1-CD3+ clones (one of which is also CD4+ and expresses V beta 8) which are constitutively responsive to the lymphokines IL-2 and IL-4. Of 11 clones tested, 7 produce IL-2 and/or IL-4 lymphokines after stimulation through the TCR, whereas 4 do not, requiring exogenous lymphokines for optimal responses to Ag. Of 10 clones tested for IL-2R expression, 3 had notably low levels, correlating with low proliferative responses to IL-2. The results reveal the spectrum of T cells available to a mouse which is congenitally athymic and describe the heterogeneity of immune defects expressed in such cells at the clonal level.     

T cell receptor gamma gene status of human alpha/beta+ and gamma/delta+ T cell clones: absence of V9JP rearrangements in alpha/beta+ clones is not a result of a lack of rearrangements involving more 5' J gamma segments

T cell receptor (TCR) gamma gene rearrangements were examined in panels of human T cell clones expressing TCR alpha/beta or gamma/delta heterodimers. Over half of the alpha/beta+ clones had both chromosomes rearranged to C gamma 2 but this was the case for only 20% of the gamma/delta+ clones. While more than half of the gamma/delta+ clones showed a V9JP rearrangement, this configuration was absent from all 49 alpha/beta+ clones analysed. However, this was not a result of all rearrangements being to the more 3' J gamma genes as 11 alpha/beta+ clones had rearrangement(s) to JP1, the most 5' J gamma gene segment. Both alpha/beta+ and gamma/delta+ clones showed a similar pattern of V gamma gene usage in rearrangements to J gamma 1 or J gamma 2 with a lower proportion of the more 3' genes being rearranged to J gamma 2 than for the more 5' genes. Several alpha/beta+ and several gamma/delta+ clones had noncoordinate patterns of rearrangement involving both C gamma 1 and C gamma 2. Eleven out of fourteen CD8+ clones tested had both chromosomes rearranged to C gamma 2 whereas all clones derived from CD4-8- cells and having unconventional phenotypes (CD4-8- or CD4+8+) had at least one C gamma 1 rearrangement. Twelve out of twenty-seven CD4+ clones also had this pattern, suggesting that CD4-8+ clones had a tendency to utilize more 3' J gamma gene segments than CD4+ clones. There was some evidence for interdonor variation in the proportions of TCR gamma rearrangements to C gamma 1 or C gamma 2 in alpha/beta+ clones as well as gamma/delta+ clones. The results illustrate the unique nature of the V9JP rearrangement in gamma/delta+ clones and the possible use of a sequential mechanism of TCR gamma gene rearrangements during T cell differentiation is discussed.     

Cutting edge: TCR delta gene is frequently rearranged in adult B lymphocytes

TCR gene rearrangement generates diversity of T lymphocytes by V(D)J recombination. Ig genes are rearranged in B cells using the same enzyme machinery. Physiologically, TCR gene is postulated to rearrange exclusively in T lineage, but malignant B precursor lymphoblasts contain rearranged TCR genes in most patients. Several mechanisms by which malignant cells break the regulation of V(D)J recombination have been proposed. In this study we show that incomplete TCR delta rearrangements V2-D3 and D2-D3 occur each in up to 16% alleles in B lymphocytes of all healthy donors studied, but complete VDJ rearrangement was negative at the sensitivity limit of 1%. Data are based on real-time quantitative PCR validated by PAGE and sequencing of the cloned products. Therefore, TCR genes rearrange not exclusively in T lineage. This study opens up further questions regarding the exact extent of the "cross-lineage" TCR or Ig rearrangements in normal lymphocytes, specific subsets in which the cross-lineage rearrangements occur, and the physiological importance of these rearrangements.     

IL-2 and a contact-mediated signal provided by TCR alpha beta + or TCR gamma delta + CD4+ T cells induce polyclonal Ig production by committed human B cells. Enhancement by IL-5, specific inhibition of IgA synthesis by IL-4.

To study the role of T cells in T-B cell interactions resulting in isotype production, autologous purified human splenic B and T cells were cocultured in the presence of IL-2 and Con A. Under these conditions high amounts of IgM, IgG, and IgA were secreted. B cell help was provided by autologous CD4+ T cells whereas autologous CD8+ T cells were ineffective. Moreover, CD8+ T cells suppressed Ig production when added to B cells cocultured with CD4+ T cells. Autologous CD4+ T cells could be replaced by allogeneic activated TCR gamma delta,CD4+ or TCR alpha beta,CD4+ T cell clones with nonrelevant specificities, indicating that the TCR is not involved in these T-B cell interactions. In contrast, resting CD4+ T cell clones, activated CD8+, or TCR gamma delta,CD4-,CD8- T cell clones failed to induce IL-2-dependent Ig synthesis. CD4+ T-B cell interaction required cell-cell contact. Separation of the CD4+ T and B cells by semiporous membranes or replacement of the CD4+ T cells by their culture supernatants did not result in Ig synthesis. However, intact activated TCR alpha beta or TCR gamma delta,CD4+ T cell clones could be replaced by plasma membrane preparations of these cells. Ig synthesis was blocked by mAb against class II MHC and CD4. These data indicate that in addition to CD4 and class II MHC Ag a membrane-associated determinant expressed on both TCR alpha beta or TCR gamma delta,CD4+ T cells after activation is required for productive T-B cell interactions resulting in Ig synthesis. Ig production was also blocked by mAb against IL-2 and the IL-2R molecules Tac and p75 but not by anti-IL-4 or anti-IL-5 mAb. The CD4+ T cell clones and IL-2 stimulated surface IgM-IgG+ and IgM-IgA+, but not IgM+IgG- or IgM+IgA- B cells to secrete IgG and IgA, respectively, indicating that they induced a selective expansion of IgG- and IgA-committed B cells rather than isotype switching in Ig noncommitted B cells. Induction of Ig production by CD4+ T cell clones and IL-2 was modulated by other cytokines. IL-5 and transforming growth factor-beta enhanced, or blocked, respectively, the production of all isotypes in a dose-dependent fashion. Interestingly, IL-4 specifically blocked IgA production in this culture system, indicating that IL-4 inhibits only antibody production by IgA-committed B cells.     

Human T cell leukemia virus type I prevents cell surface expression of the T cell receptor through down-regulation of the CD3-gamma, -delta, -epsilon, and -zeta genes

Infection and transformation by human T cell leukemia virus type I (HTLV-I) up-regulates expression of several inducible genes including those coding for cytokines involved in the proliferation of normal and leukemic T cells. We demonstrate that HTLV-I can also shut off expression of the CD3-gamma, delta, epsilon, and zeta genes that code for the constant elements of the TCR for Ag. In addition, the T cell-specific CD3-epsilon enhancer was found to be inactive in a HTLV-I-infected T cell clone. This HTLV-I-infected T cell clone (827-p19-II) that could be cultured in the absence of IL-2 lacked the CD3 proteins but did express the TCR-alpha and -beta proteins intracellularly. In the absence of the CD3-gamma, delta, epsilon, and zeta polypeptide chains the disulfide bridged TCR-alpha/beta heterodimer was not formed and the Ag receptor did not appear at the cell surface. These results allowed two major conclusions: first, HTLV-I infection has an effect on the T cell specific regulatory elements that coordinately regulate CD3-gamma, delta, epsilon, and zeta expression and second, the CD3-gamma, delta, epsilon, and zeta proteins are necessary for formation and routing the variable TCR-alpha/beta (or -gamma/delta) heterodimer to the human T cell surface.     

Abnormal T cell development in CD3-zeta-/- mutant mice and identification of a novel T cell population in the intestine.

The T cell antigen receptor (TCR)-associated invariable membrane proteins (CD3-gamma, -delta, -epsilon and -zeta) are critical to the assembly and cell surface expression of the TCR/CD3 complex and to signal transduction upon engagement of TCR with antigen. Disruption of the CD3-zeta gene by homologous recombination resulted in a structurally abnormal thymus which primarily contained CD4- CD8- and TCR/CD3very lowCD4+CD8+ cells. Spleen and lymph nodes of CD3-zeta-/- mutant mice contained a normal number and ratio of CD4+ and CD8+ single positive cells that were TCR/CD3very low. These splenocytes did not respond to antibody cross-linking or mitogenic triggering. The V beta genes of CD4-CD8- and CD4+CD8+ thymocytes and splenic T cells were productively rearranged. These data demonstrated that (i) in the absence of the CD3-zeta chain, the CD4- CD8- thymocytes could differentiate to CD4+CD8+ TCR/CD3very low thymocytes, (ii) that thymic selection might have occurred, (iii) but that the transition to CD4+CD8- and CD4-CD8+ cells took place at a very low rate. Most strikingly, intraepithelial lymphocytes (IELs) isolated from the small intestine or the colon expressed normal levels of TCR/CD3 complexes on their surface which contained Fc epsilon RI gamma homodimers. In contrast to CD3-zeta containing IELs, these cells failed to proliferate after triggering with antibody cross-linking or mitogen. In comparison to thymus-derived peripheral T cells in the spleen and lymph nodes, the preferential expression of normal levels of TCR/CD3 in intestinal IELs suggested they mature via an independent extrathymic pathway.     

Isolation, characterization, and expression of cDNA clones encoding the mouse Fc receptor for IgE (Fc epsilon RII)1

We have isolated cDNA clones encoding a mouse low affinity receptor for IgE (Fc epsilon RII) from a cDNA library of BALB/c splenic B cells activated with LPS and IL-4. The 2.2-kb cDNA clone encodes a 331 amino acid membrane glycoprotein that is homologous to human Fc epsilon RII (CD23) and a family of carbohydrate-binding proteins. COS7 cells transfected with the cDNA clones expressed a 45,000 m.w. protein that bound IgE and the anti-Fc epsilon RII mAb, B3B4. Fc epsilon RII mRNA was up-regulated in mouse B cells by culture with IL-4, but not in B cells cultured with IgE. Fc epsilon RII mRNA was detected in IgM+/IgD+ B cell lines, but not in pre-B cell lines or in B cell lines which have undergone differentiation to secrete Ig. The monocyte line P388D1, mast cell lines MC/9 and PT18, and peritoneal macrophages stimulated with IL-4 lacked detectable Fc epsilon RII mRNA, as did Thy-1.2+, CD4+, and CD8+ normal T cells and Thy-1.2+ T cells from Nippostrongylus brasiliensis-infected mice.     

Characterization of a cloned ultraviolet radiation (UV)-induced suppressor T cell line that is capable of inhibiting anti-UV tumor-immune responses

Ultraviolet radiation (UV) is a potent carcinogen for the induction of skin tumors. In this regard, UV represents a unique carcinogenic agent, in that depending on the dosage and conditions of administration it can function as either a complete carcinogen, a carcinogenic promoting agent, or an immunologic modulator of anti-tumor rejection responses. The immunologic modulatory activity of UV has been demonstrated in numerous studies. These studies have shown that subcarcinogenic doses of UV induce a population of suppressor T lymphocytes (Ts cells) that allow for the emergence and progression of UV-induced tumors. Although the phenotypic and functional properties of these cells have been established, it was unclear as to whether the UV-induced Ts cell population consisted of multiple Ts cell clones able to recognize a range of unique tumor antigens or a limited number of Ts cell clones with functional specificity directed toward a common tumor-associated antigen (TAA). To address this question, an interleukin 2-dependent, UV-induced cloned Ts cell line was derived, by limiting dilution without exogenous antigen stimulation, from the splenic T cell population of a C3H mouse that had been exposed to a subcarcinogenic dose of UV. This Ts cell line, designated UV2.10, was selected for its ability to suppress the in vitro differentiation of cytotoxic T cells from the draining lymph nodes of UV-induced tumor-immune mice. When transferred into non-UV-irradiated syngeneic mice, which normally reject a UV-induced tumor implant, the UV2.10 cells rendered their hosts susceptible to the growth of a battery of UV-induced tumors. Although capable of suppressing in vitro and in vivo UV-induced tumor-immune responses, UV2.10 cells did not inhibit the elicitation of contact hypersensitivity responses, the rejection of allogeneic skin grafts, responses, the rejection of allogeneic skin grafts, or the rejection of allogeneic UV-induced tumors. These data suggest that the cloned UV2.10 Ts cell line possesses functional antigenic specificity that may be limited to the regulation of immune responses that are directed toward the TAA expressed by syngeneic UV-induced tumors. Employing monoclonal antibodies and FACS analysis, the cell surface phenotype of the UV2.10 cell line was determined to be: Thy-1.2+, Lyt-1-, Lyt-2+/- (dim), L3T4a-, I-A/E-, and I-J+. This cell surface phenotype is indicative of a suppressor T cell. These data lend further support to the hypothesis that the UV-induced Ts cell population is clonal in nature and functions through its ability to recognize a common TAA(s) that appears to be expressed by virtually all UV-induced tumors.