Properties of reticulum cell sarcomas in SJL/J mice. VII. Nature of normal lymphoid cells proliferating in response to tumor cells

Cyclophosphamide treatment of an SJL murine B-cell lymphoma increases the proportion of suppressive CD8+ over tumor-stimulatory CD4+ T-lymphocytes

Lymphomas (formerly reticulum cell sarcomas (RCS)) which develop spontaneously in SJL mice are a murine counterpart of human low grade B-cell non-Hodgkin's lymphoma. Tumor cells stimulate proliferation of syngeneic CD4+ T-lymphocytes which secrete cytokines required for tumor growth. Cyclophosphamide treatment of tumor-bearing mice (RCS/Cy) decreases in vitro tumor-stimulated CD4+ T-cell proliferation and, in turn, tumor growth, in part, through the suppressive action of CD8+ T-lymphocytes. In RCS/Cy compared to untreated tumor-bearing (RCS5) mice we report marked in vivo decreases in: (1) the activation (CD44HI/CD45RBLO phenotype) and proliferation (S + G2M phases of the cell cycle) of CD4+ T-lymphocytes; (2) the ratio of activated and/or proliferating CD4+ to CD8+ T-lymphocytes, and; (3) the proliferation of tumor cells. Also, depletion of CD8+ T-lymphocytes from RCS/Cy mice abrogated much of the efficacy of the RCS/Cy treatment and led to changes in lymphoid populations more reminiscent of those in RCS5 than RCS/Cy mice. The data support our hypothesis that the RCS/Cy treatment achieves its efficacy by preventing the predominance of CD4+ over CD8+ T-lymphocytes which is essential to maximum tumor growth in RCS5 mice. The results imply that analogous B-cell lymphomas in humans also may be treatable by shifting the T-cell balance toward inhibitory CD8+ rather than the tumor-stimulatory CD4+ T-lymphocytes.

IL-10 production in a CD5+ B cell lymphoma arising in a CD4 monoclonal antibody-treated SJL mouse

A majority of SJL mice develop spontaneous reticulum cell sarcomas (RCS) at about 1 year of age which can be transplanted into young SJL recipients. Previous studies have shown that RCS tumors are of B cell lineage, and that the development of these lymphomas and their subsequent growth depends upon host-derived T helper cell factors. In vivo treatment of SJL mice with anti-CD4 monoclonal antibody (mAb) prevents the development of the characteristic B lymphomas. Most of the mAb-treated animals were tumor free and had a significantly prolonged life span. However, one such CD4 mAb-treated mouse developed a transplantable IgM+ CD5+ B cell lymphoma (designated NJ101), which has not previously been described in SJL/J mice. NJ101 is clonal on the basis of a discrete non-germ line Ig heavy chain gene rearrangement by Southern blot analysis. Unlike the sIg- CD5- transplantable RCS-X cell line, the IgM+ CD5+ NJ101 lymphoma cells will grow in immuno-compromised hosts, such as irradiated recipients or in recipients treated with CD4 mAb in vivo. The RCS (B cell) lymphoma requires CD4+ T cells for progressive growth, whereas the growth of the CD5+ B lymphoma cells is enhanced by the removal of such cells. Thus, CD5+ B cell clonal development may be aided by the removal of regulatory T cells and/or the malignant CD5+ B cells may produce their own growth factors in an autocrine manner. Examination of IL-10 message by quantitative polymerase chain reaction techniques indicate that the CD5+ B lymphoma cells produce increased levels of IL-10 relative to normal LN cells or purified RCS lymphoma cells. These results suggest that two different types of B cell tumors, both of which can develop in SJL mice, have different growth requirements. Furthermore, treatment to prevent the occurrence of the characteristic RCS malignancy of SJL mice may lead to the development of another form of B cell neoplasia.

I-E expression does not by itself influence growth of or T cell unresponsiveness to SJL lymphomas

The nature of the antigen on SJL lymphoma (reticulum cell sarcomas, RCS) cells that is strongly stimulatory to syngeneic CD4+ T cells is still elusive. Previously, we showed that the response to RCS of T cells from F1 hybrids of SJL by strains expressing I-Ak,d and/or I-Ek,d was much lower than that of T cells from SJL mice or from F1 hybrids of SJL by H2b- or H2s-bearing strains. We now show that removal of CD8+T cells from the responding cell population of (SJL x BALB/c)F1 or (SJL x A.TL)F1 mice does not enhance their responses, suggesting that the negative effect of H2k,d is not due to suppressor cells. Moreover, repeated injections of RCS cells into such F1 mice also fail to enhance the response, suggesting that these mice lack responder cells. T cells from I-E alpha transgenic (C57BL x SJL)F1 mice backcrossed to SJL respond to RCS as do T cells from I-E alpha- littermates or SJL mice. Similarly, I-E alpha+ SJL mice support RCS growth in vivo to the same (LN + spleen)/body weight ratio as do I-E- littermates. Thus, while I-E appears to have a negative influence on T cell responsiveness and RCS growth in F1 mice, it does not have such an effect when present, by itself, on a SJL background. The role of V beta 17 a+ T cells in the response of SJL T cells to RCS was also examined, because such cells are known to be responsive to I-E. The responses of V beta 17a(+)-depleted (0.3% V beta 17 a+) and V beta 17 a(+)-enriched (25.3% V beta 17a+) SJL T cell populations to RCS were examined by limiting dilution. We found the incidence of responding cells to be slightly higher in the depleted (0.016%) than in the (0.006%) enriched population. Furthermore, lymph node blast cell populations responding to RCS do not exhibit a higher percentage of cells staining for V beta 17a than do blast cells responding to Con A or unstimulated lymph node cells.

CD8 suppressor cell activity and its effect on CD4 helper cell-dependent growth of SJL/J B-cell lymphomas

CD8 cells, flow cytometrically sorted from the lymph nodes of tumor-bearing and normal SJL/J mice, suppressed in vitro proliferation of syngeneic CD4 cells in response to concanavalin A, two independent SJL/J lymphomas, and LPS-activated syngeneic B-cell blasts. The data confirm earlier reports that nonspecific suppressor cells are generated as a consequence of SJL/J lymphoma-stimulated T-cell proliferation. Earlier reports are extended, in that the suppressor cell is identified as expressing CD8, and the suppressor activity is shown to decrease the tumor-stimulated CD4 cell proliferation which is essential to growth of these CD4-dependent murine B-cell lymphomas. In three separate experiments, anti-CD8 treatment of mice, in which CD4 cells were made limiting by injection with anti-CD4, increased growth of transplantable SJL/J lymphomas with corresponding increases in numbers of CD4 cells. The data imply that, under certain conditions, CD8 suppressor cells measurably influence growth of SJL/J lymphomas by regulating the tumor-stimulated CD4 cell proliferation essential to maximum growth of SJL/J lymphomas.

T-helper-cell-specific monoclonal antibody inhibits growth of B-cell lymphomas in syngeneic SJL/J mice

Transplantable follicular center cell lymphomas of SJL/J mice are B-cell tumors that stimulate proliferation of host T-helper (TH) cells and which grow progressively in the peripheral lymphoid tissues of immunocompetent recipients. However, tumor growth is compromised in immunosuppressed syngeneic recipients, suggesting that the host response to SJL follicular center cell (SJL/FCC) lymphoma cells is required for optimal tumor growth. In vitro studies indicate that the host TH cells (Lyt-1+, 2-, L3T4a+) which respond to the major histocompatibility complex (MHC) class II (I-As) surface determinants on the SJL/FCC lymphoma cells produce a variety of lymphokines, some of which may promote tumor growth in vivo. The results of this study demonstrate that treatment of lymphoma-injected mice with L3T4a-specific mAb inhibits the growth of the SJL/FCC lymphoma cells, despite the fact that these tumor cells do not express L3T4a determinants. Thus, in this model, mAb therapy targeting host immune cells rather than the tumor cells is an effective means to control tumor growth. Long-term observation of SJL/FCC lymphoma-injected, anti-L3T4a mAb-treated mice reveals prolonged survival of the majority of these animals with periodic recurrence of tumor growth. During periods of remission, LN cells from these long-term surviving animals were unable to mount the characteristic in vitro host response to irradiated SJL/FCC lymphoma cells. These results provide direct evidence that SJL/FCC lymphoma cells fail to retain their characteristic neoplastic properties in a microenvironment that is initially devoid of tumor-responsive TH cells.

Characterization and growth factor requirements of SJL lymphomas. II. Interleukin 5 dependence of the in vitro cell line, cRCS-X, and influence of other cytokines

Follicular B cell lymphomas of SJL mice [reticulum cell sarcoma (RCS)] are dependent on syngeneic Ly-1+,2- T cells for their growth. These T cells produce a number of lymphokines in response to stimulation with gamma-irradiated RCS cells including interleukin (IL) 2, interferon-gamma (IFN-gamma), IL4 and IL5, some of which may be required for growth of the tumor. Previous studies have shown that an RCS cell line, cRCS-X, can be maintained in vitro indefinitely, if the cultures are supplemented with gamma-irradiated lymph node (LN) cells or with a preparation of human B cell growth factor (BCGF). In the present studies, the growth requirements of this cell line were analyzed in more detail in short-term assays of both [3H]thymidine incorporation and colony formation in agarose. Recombinant murine IL5 cause dose-dependent proliferation of cRCS-X cells similar to that induced with BCGF. The level of colony formation by cRCS-X cells induced by optimal concentrations of BCGF was not increased further by the addition of IL5, suggesting that the two factors act via a common mechanism. IL1 and IFN-gamma each enhanced cRCS-X proliferation induced by BCGF or IL5 in both assays. The effects of IL1 plus BCGF, IFN-gamma plus BCGF, and IL1 plus IL5 were clearly synergistic. Preincubation of cRCS-X cells with IL1 enhanced their ability to proliferate in response to BCGF or IL5 in [3H]thymidine incorporation assays, but the reverse sequence of cytokine addition showed no effect of IL1. No such effect was seen with IFN-gamma. Indeed, IL1 and IFN-gamma appeared to affect BCGF-induced cRCS-X growth by different mechanisms and their combined effects were greater than that of IL1 or IFN-gamma added separately. None of the other cytokines studied, including IL2, IL3, IL4, IL6, tumor necrosis factor-alpha, granulocyte monocyte-colony-stimulating factor or transforming growth factor-beta, had any detectable effect on cRCS-X cells, either alone or in combination with BCGF or IL5. Like IL5, SJL gamma-irradiated LN cells induced cRCS-X colony-forming units (CFU) in a dose-dependent manner. IL1, or the combination of IL1 plus IFN-gamma, clearly synergized with LN cells in the induction of cRCS-X CFU, suggesting that LN cells contribute IL5. The level of CFU induced by an optimal dose of BCGF was enhanced further in the presence of LN cells and IL1.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo growth inhibition of Ia+ lymphomas in SJL mice treated with I-As-reactive monoclonal antibody

SJL/J mice injected with a syngeneic, I-As-positive transplantable lymphoma (RCS) and treated with I-As-reactive monoclonal antibody (McAb) for one week showed reduced tumor growth in peripheral lymph nodes and spleen when compared to untreated controls. The effect of McAb on RCS growth was observed after treatment with I-As McAb derived from two different hybridomas, but similar growth inhibition did not occur in RCS-injected mice treated with a non-cross-reacting I-Ab McAb. Specificity of the effect was also indicated by the observation that partial absorption of I-As McAb with I-As-positive cells decreased its ability to reduce tumor growth in RCS-injected SJL recipients. In parallel experiments in which McAb treatment was stopped after one week, RCS-injected mice survived up to 8 times longer (80 days) than untreated control mice, which died by day 10 after tumor cell inoculation. Although the precise mechanism(s) by which McAb treatment influences RCS growth has not been fully characterized, it is likely that I-As McAb may block the characteristic T cell proliferative response to I-A antigens on RCS cells that appears necessary for progressive tumor growth in vivo. Absence of such host immune recognition could result in either a deficiency in production of RCS growth-promoting lymphokines or induction of effector cells capable of inhibiting tumor growth.

Ia-restricted interaction between normal lymphoid cells and SJL lymphoma (RCS) leading to lymphokine production. I. Enhancement and suppression of antibody formation to TI antigens by supernatants and cells from cocultures of RCS and lymphoid cells

Addition of gamma-irradiated reticulum cell sarcoma (RCS) cells causes suppression of the antibody response to trinitrophenyl (TNP)-keyhole limpet hemocyanin (KLH)-primed syngeneic SJL spleen cells to TNP-polyacrylamide (PAA) in vitro. The response of anti-brain antigen (BAT) + C-treated spleen cells is not suppressed by gamma-RCS, but is suppressed by cells from 48-hr SJL lymph node or thymus + gamma-RCS cultures. Addition of as few as 2.5 x 10(5) cultured (anti-I-A + C treated to remove gamma-RCS) cells causes significant inhibition of the responses of both syngeneic and allogeneic spleen cells. Treatment of gamma-RCS-induced suppressor cells with anti-BAT + C reduces their suppressive activity. In contrast to the cells, supernatants (SN) from (lymph node (LN) + gamma-RCS) cultures greatly enhance, in an antigen-dependent fashion, the responses of untreated or anti-BAT + C-treated Sephadex G10-passed spleen cells to TNP-PAA. TNP-SIII polysaccharide, or TNP-Ficoll, but not as much to TNP-KLH. Addition of SN as late as Day 3 of culture still causes about half as much enhancement as leaving SN in throughout the culture period, but it has no effect if left with the spleen cells for only the first day of culture. SN contains high levels of IL-2 and IFN-gamma; absorption with cells from an IL-2-dependent cytotoxic T-cell line removes the enhancing activity, while treatment with pH 2 to remove the IFN-gamma has no effect. SN from an IL-2-producing T-cell line (LBRM-33) has a similar effect on antibody production to TI antigens as does SN of (LN + gamma-RCS). The results suggest a marked dependency of PFC responses to TI antigen on IL-2 in all strains examined, including SJL, LAF1, DBA/2Ha, and CBA/N, probably through a direct activation of B cells. The findings also suggest that suppressor T cells, induced by gamma-RCS in syngeneic lymphoid cells, absorb the IL-2 needed for responses to TI antigens in vitro.

Natural killer cell activity in reticulum-cell sarcomas of SJL/J mice. II. Analysis of RCS-associated NK activity

Lymphoid cells taken from the grossly enlarged lymph nodes (LN) and spleens of SJL/J mice bearing transplantable reticulum-cell sarcomas (RCS), showed increased levels of natural killer (NK) cell activity, when compared to LN and spleen cells taken from normal SJL mice. The NK susceptible target cells used for these studies included RLmale-1 and YAC-1. Target cells that were not susceptible to NK lysis by CBA/J effector cells (high NK strain) were also resistant to lysis by RCS tumor cells. Although significant lysis of target cells was detectable at 4 h, optimal NK cytotoxicity was observed in a 16-h 51Cr-release assay. In terms of lytic units (LU)/10(7) effector cells, greater NK activity was observed in RCS effectors than was apparent in normal CBA/J lymphoid cells. Depletion of macrophages from RCS cell preparations had no effect on the observed NK activity. Purified Mu-IFN-alpha stimulated a small increase in the NK activity expressed by SJL lymphoid cells; however RCS-derived supernatants (containing Mu-IFN-gamma) did not augment NK activity of SJL effector cells, nor were they cytotoxic for NK target cells, Therefore, tumor-derived soluble factors appear not to be involved in the observed RCS-associated NK activity. The data presented in this report further define the parameters of the NK activity manifested by RCS tumor cell preparations. The accompanying article characterizes the nature of the NK effector cells present within RCS tumors of SJL mice. Taken together, these data indicate that the RCS tumors represent either neoplastic expansion of conventional NK cells with somewhat modified properties, or else an entirely new class of cytotoxic effector cells.

Expression of hybrid Ia molecules on the cell surface of reticulum cell sarcomas that are undetectable on host SJL/J lymphocytes

SJL/J (H-2 (8)) lymphocytes, primed in vitro against primary, cultured, and transplantable syngeneic reticulum cell sarcomas (RCS) were found to recognize and bind to the tumor without subsequent cytolysis. Additional data showed that the recognition was also directed against Ia molecules of the H-2(d), but not H-2(k), haplotype. Normal spleen cells of DBA/2, B 10.D2, and B 10.OL mice were bound, whereas those of CBA, B 10.BR, B 10.A, B 10.GD, and D2.GD were not. Furthermore, the Ia molecules were in the form of a hybrid, because spleen cells from F(1) progeny of a B10.A and a B10.GD parent were recognized and bound as effectively as the RCS. Recognition was not restricted solely to the H-2(d) haplotype. Spleen cells from B10.S(9R) mice were also significantly bound. This result suggested that the RCS expresses a hybrid Ia molecule containing a beta-chain of the H-2(8) haplotype. Recognition of this hybrid Ia molecule by the host resulted in a cross- reactive recognition of H-2(d) specificities. Further analysis revealed that the RCS express on their cell surface an alpha-chain of the hybrid Ia molecule which is involved in host anti-tumor recognition. Preincubation of the RCS with monoclonal antibody directed against the Ia.7 specificity on the alpha-chain could block lymphocyte-to-tumor cell binding. The blocking activity could be removed by preabsorption of the antibody on the RCS, as well as normal Ia.7-bearing lymphocytes, but not on lymphocytes that do not express Ia.7, such as SJL/J. The data suggest that the hybrid Ia molecules expressed on the RCS, and recognized by tumor-primed syngeneic lymphocytes, are composed of both a syngeneic and an alien chain. The component alien to the SJL/J host is the Ia.7-bearing alpha-chain. Normal SJL/J cells synthesize but do not express the beta-chain. In the RCS, however, alien alpha-chain synthesis permits expression of the syngeneic beta-chain in the form of a hybrid Ia molecule.

Growth of SJL/J-derived transplantable reticulum cell sarcoma as related to its ability to induce T-cell proliferation in the host. I. Dominant negative genetic influences of other parent haplotype in F1 hybrids of SJL/J mice

Growth of three transplantable reticulum cell sarcomas (RCS) was studied in a variety of F1 hybrids of SJL/J mice by determination of lymph node (LN) and spleen: body weights ratios 7 and 14 d after intravenous injection of RCS cells. Comparison of BIO.S x SJL and A.SW x SJL with SJL/J showed a negative effect of both the A and the BIO non-H-2 genes, particularly on growth in LN. F1 hybrid resistance was noted with F1 hybrids that carried H-2Dd and was much more evident with F1 hybrids from BIO- than from A-background mice. This resistance was less marked at 14 than at 7 d and was partially overcome by injection of higher tumor doses. Changing the I region in the F1 parent from H-2d to H-2b or H-2f had no effect on growth, but changing to H-2k or H-2d virtually abolished the ability to support tumor growth. This effect appeared partially as a result of the I-E/C and partially of the I-A(B) region and was not overcome by higher tumor dose or longer intervals after injection. There also appeared to be a negative influence on growth of H-2Kk, but this was difficult to differentiate from the I-Ak effect with the available strains. The known proliferative responsiveness that SJL/J Lyt-1 T cells exhibit to Ia determinants on gamma-irradiated RCS cells in vitro was also compared with that of cells from various F1 hybrids. Responsiveness of F1 LN cells was expressed as a percentage of the response in SJL/J LN cells to the same RCS cells, measured as [3H]thymidine incorporation. There was a striking degree of correlation between proliferative responsiveness of F1 LN cells to RCS and the ability of the F1 mice to support tumor growth. This correlation was especially clear with respect to the negative influences of non-H-2 genes, and of H-2 loci in the I region, particularly of I-Ak or -d and of I-E/Ck or -d, but there also appeared to be a (smaller) negative effect of I-Ab or -f. Negative influence of H-2Dd on growth, however, was not reflected in a similarly large effect on the proliferative response. Additional findings showed that LN cells from all F1 hybrids exhibited equivalent syngeneic mixed lymphocyte responses in the presence of polyethylene glycol to mitomycin-treated spleen cells from both the SJL/J and the other parent. The extra high response of F1 cells to RCS cells, as compared with SJL spleen cells, however, was always absent when Ik or -d was contributed by one of the F1 parents. The results suggest a promoting effect of the proliferative response on RCS growth in vivo and, furthermore, an interesting effect of I-A and I-E/C genes, possibly via an interaction product, on the ability of LN cells to be stimulated by Ia determinants on RCS cells.