Thymus-derived lymphocyte-dependent rejection of syngeneic papovavirus (SV40) and methylcholanthrene tumors in inbred hamsters.

Treatment of specifically sensitized MHA hamster lymphoid cells with rabbit antisera specific for hamster thymus-derived lymphocytes, in the presence of C, eliminated those cells capable of inhibiting the growth of syngeneic SV40 and methylcholanthrene tumors in vivo. Thymectomized, lethally-irradiated, bone marrow-reconstituted hamsters, shown to be devoid to T cell function, were, after attempted specific sensitization to the two syngeneic tumor cell lines, unable to reject either tumor by direct challenge in vivo. In addition, lymphocytes from such animals were incapable of inhibiting the growth of either tumor cell line in normal syngeneic recepients in the tumor cell neutralization assay. These data strongly support the conclusion that specifically sensitized thymus-derived lymphocytes are required for the rejection of syngeneic SV40 and methylcholanthrene tumors in inbred hamsters.     

Cell-mediated immunity to chemically xenogenized tumors I. Inhibition by specific antisera and H-2 association of the novel antigens

Summary T cell-mediated proliferative and cytotoxic responses occur in vitro to syngeneic tumor cells antigenically altered by mutagen treatment. One such xenogenized variant of the murine L5178Y lymphoma elicits IgG antibodies reactive with determinants on variant cells that are not expressed at detectable levels on parental or normal cells of the same H-2^d haplotype and are also unrelated to public specificites of H-2^b or H-2^k histocompatibility antigens. In the present study we investigated the effect of those antibodies on development of cell-mediated responses in vitro to the xenogenized cells used for induction of the humoral response. The proliferative reaction, generation of cytolytic activity and target cell lysis were all inhibited by the anti-xenogenized tumor immune serum, whereas the corresponding reactions to the parental cells by syngeneic or allogeneic effector lymphocytes were not. In order to investigate the possible H-2 association of T cell-mediated responses to xenogenized cells, we also examined the effect on those reactions of antibodies specific for Class I or Class II products of the H-2^d complex. The results obtained suggested a role for I-A^d molecules in the T cell proliferative response to the xenogenized cells, and also indicated a preferential association of the cytotoxic response with H-2K^d determinants.     

Synergy between subpopulations of normal mouse spleen cells in the in vitro generation of cell-mediated cytotoxicity specific for "modified self" antigens.

Responding lymphoid cells cultured in vitro with irradiated trinotrophenyl (TNP)-modified syngeneic spleen cells develop direct cell-mediated cytotoxicity which is specific for target cells bearing both the TNP moiety and histocompatibility determinants of the modified sensitizing cell. Two subpopulations of normal mouse spleen cells have been shown to synergize in the in vitro generation of specific cell-mediated cytotoxicity to these "modified self" antigens. The synergizing populations are nylon wool column-adherent and column-nonadherent fractions of normal mouse spleen. When mixtures of these two cell populations are cultured in vitro with irradiated TNP-modified syngeneic spleen cells, greater cytotoxicity is generated in the two populations sensitized separately. The synergizing cell in the column-adherent population is resistant to lysis by rabbit anti-mouse brain serum, is distinct from the cytotoxic effector T lymphocyte, and is unresponsive to phytohemagglutinin; its synergizing function could not be replaced by peritoneal cells. These results suggest that it is a non-T cell which may be distinct from the macrophage.     

Augmentation of immune response to syngeneic fibrosarcoma T241 with in vivo protection

Summary Lewis T241 fibrosarcoma, a syngeneic tumor in C57 BL/6J mice, was found to be poorly immunogenic. When tumor-bearing animals (TBA) were challenged with tumor cells either concomitantly or after excision of a growing tumor no protection was observed. In vivo (Winn) neutralization assays also showed a lack of tumor immunogenicity. However, in vitro studies showed that a significant proliferative response could be elicited from the spleen cells of TBA when these cells were cultured with either mitomycin-C-treated tumor cells or KCl tumor extract. Similarly, macrophage migration inhibition factor (MIF) was produced by TBA spleen cells upon incubation with KCl tumor extract, but no cell-mediated cytotoxicity to T241 target cells was observed with various lymphoid cell populations at any stage of tumor growth. Immunization of syngeneic animals with Vibrio cholerae neuraminidase(VCN)-treated, irradiated tumor cells alone or admixed with Freund's complete adjuvant (FCA) resulted in decreased tumor growth and fewer pulmonary metastases following challenge with 10⁶ tumor cells. No complete tumor rejection was observed. In contrast, 13 of 16 animals immunized with irradiated tumor cells admixed with FCA rejected 10⁵ tumor cells. Animals that grew tumors had significantly reduced tumor growths and pulmonary metastases. Lymph node and peritoneal exudate cells (PEC) of immunized animals showed significant cytotoxicity to T241 cells.     

Nonspecific inhibition of tumor growth in vivo by admixed allogeneic tumor-sensitized lymphoid cells and identical inactivated allogeneic tumor cells.

With the in vivo tumor neutralization test (Winn test), growth of a transplanted (KMT-17) from Wistar-King-Aptekman rats was inhibited by allogeneic tumor (AH-66 from Donryu rats)-sensitized syngeneic lymphoid cells admixed with mitomycin C (MMC)-treated AH-66 cells. The observed tumor inhibition may be immunologically nonspecific, since no cross-antigens were detected by membrane immunofluorescence on the surfaces of KMT-17 and AH-66 cells. Close contact among KMT-17, AH-66-sensitized lymphoid cells and MMC-treated AH-66 cells was required for the inhibition of KMT-17 growth. AH-66 cells pretreated with formalin or ultrasonication lost tumor inhibitory activity when they were admixed with AH-66-sensitized lymphoid cells, and only MMC-treatment effectively preserved the tumor inhibitory activity of AH-66 cells. The sensitized spleen cells, draining lymph node, or peripheral blood cells inhibited tumor growth when they were admixed with MMC-treated AH-66 cells, whereas nucleated cells from bone marrow, thymus, or distal lymph node did not. Growths of KMT-17 were inhibited by admixed sensitized spleen cells and MMC-treated AH-66 even when pre-irradiated rats were used as recipients.     

Generation of suppressor lymphocytes during sensitization in culture against a syngeneic tumor: affinity chromatography on insolubilized histamine

We investigated the effect of depletion of histamine-binding lymphoid cells on immunological properties of lymphocytes sensitized in culture against tumor cells. C57BL/6 spleen cells that were sensitized in vitro on monolayers of the syngeneic Lewis lung carcinoma (3LL) became cytotoxic to the tumor cells in vitro after 3 to 5 days of sensitization. Sensitized cells harvested after 4 days of sensitization occasionally enhanced tumor growth in vivo. Fractionation of the sensitized lymphocytes over insolubilized histamine-rabbit serum albumin-Sepharose (HRS) columns decreased or abolished the enhancing activity in vivo and specifically increased the in vitro cytotoxic activity of the depleted lymphocytes. A similar increase in the cytotoxic activity of HRS-fractionated cells was observed in an allogeneic combination of C57BL spleen cells sensitized against C3H fibroblasts. The effect of HRS chromatography on the in vitro cytotoxic activity increased with prolonged incubation of the depleted effector cells with the target cells.     

A rapid method for quantitation of immunofluorescence on human lymphoblastoid cell suspensions.

A quantitative fluoroimmunoassay for antibodies to, and surface antigens of, human lymphoblastoid cells (IM-1) with photon-counting spectrofluorometry is described. IM-1 cell suspensions were reacted with rabbit antiserum to human spleen vesicular membranes, were washed, and then were reacted with an excess amount of fluorochrome-conjugated (fluorescein or rhodamine) goat anti-rabbit immunoglobulin G (IgG). Under appropriate conditions, antibodies to IM-1 cells could be detected with experimental/control fluorescence ratios ranging between 5 and 40. Moreover, detectable levels of antibody-saturated cells approached 5 × 10³ cells per milliliter or a total of 1.7 × 10³ cells per assay. Inhibition of the fluoroimmunoassay was performed with either viable IM-1 cells or IM-1 vesicular membrane preparations and demonstrated a dose-dependent antigen inhibition. Fluorescence of sensitized cells reactive with either fluorescein- or rhodamine-labeled antiglobulins could be quantitatively distinguished in dual-labeled preparations.     

The immune response to a chemically induced fibrosarcoma

Summary A clone of C3H10T 1/2 fibroblasts transformed in vitro with the carcinogen 3-methylcholanthrene readily produced tumors when as few as 10³ cells were injected into immunocompetent adult syngeneic mice. A non-transformed clone of the same parentage did not produce tumors. Because the cell-mediated immune response has an important role in inhibiting the growth of tumors, we have compared the ability of both these transformed and non-transformed fibroblasts to stimulate and to act as targets in cell-mediated cytotoxicity (CMC) assays. This model is unique in that studies of the immune response to tumors rarely have or utilize appropriate normal controls. When both types of irradiated fibroblasts were used as stimulators in vitro, neither syngeneic nor allogeneic effector spleen cells capable of efficiently lysing the tumor fibroblasts were generated. In contrast, the normal fibroblasts could both stimulate and be lysed by allogeneic cytolytic T cells (CTL). However, the tumor fibroblasts could be lysed by allogeneic effector spleen cells that had been sensitized to C3H/He spleen cells. These results suggest that the expression of alloantigenic determinants necessary for stimulating a CMC response may vary substantially among normal cell types. They further indicate that the tumor cells are not resistant to lysis by appropriately stimulated effector cells. Thus, they must express antigenic determinants necessary for immune lysis and they do not inhibit the functional expression of cytolytic cells once generated. Consequently, tumor growth in vivo may be dependent, in part, upon a failure of the syngeneic host's immunocompetent cells to respond appropriately to the tumor cells. Additional data are provided which suggest that this failure is attributable in large part to immunosuppressive properties of the tumor cells.     

Responsiveness of Thymus Cells to Syngeneic and Allogeneic Lymphoid Cells

THE thymus is necessary for the normal development of cell-mediated immunity in mice as shown by the immunological defects after neonatal thymectomy¹. Thymus cells themselves can be stimulated by allogeneic lymphoid cells in mixed leucocyte reaction (MLR)² and become killer cells or cytotoxic lymphocytes after stimulation with allogeneic spleen cells in vitro (H. Wagner and M. Feldmann, unpublished work) and in vivo^3,4. This suggests that the thymus as well as peripheral lymphoid tissues contain T cells which can be stimulated by foreign histocompatibility antigen to divide and differentiate into the cytotoxic lymphocytes which mediate cellular immunity. There have been suggestions that thymus cells might be stimulated to divide by “self” antigen, as well as foreign cells: incorporation of ³H-thymidine above background levels has been found in cultures with syngeneic spleen and thymus cells of adult rats⁵, although the experiments do not determine whether thymus or spleen cells have been stimulated. In contrast to these experiments, Howe et al. reported that only thymus cells of neonatal CBA mice reacted to allogeneic and syngeneic spleen cells of adult animals in “one way” MLR cultures^6,7. Whether the reaction of neonatal thymus cells to syngeneic adult spleen cells is recognition of “self” antigens is uncertain, since spleens of adult mice could carry antigens which do not occur in neonatal animals and are therefore “unknown” for neonatal thymus cells. We demonstrate here that neonatal thymus cells do not react to 4-day-old CBA spleen cells, but adult thymus cells do react against both allogeneic and syngeneic adult spleen cells.     

In vitro induction of cell-mediated immunity to murine leukemia cells

Summary An adoptive chemoimmunotherapeutic model based on the use of chemotherapy and lymphocytes specifically sensitized against tumor cells in vitro was tested in mice transplanted with syngeneic leukemia cells. C57BL/6 and A strain mice were inoculated i.p. or i.v. (day 0) with lethal doses (1×10³–1×10⁵) of EL4 and YAC leukemia cells, respectively. Leukemic mice were subsequently treated (day 1 or day 3) with partially curative doses (80–140 mg/kg) of cyclophosphamide (Cy), followed by i.p. or i.v. administration of 1–3×10⁷ cytotoxic lymphocytes (CL) induced in macro-mixed leukocyte-tumor cell cultures (MLTC). The following results were obtained: untreated mice died with tumor within 20 days; mice receiving sensitized lymphocytes only showed a modest prolongation of survival and only 5–15% of the animals were cured; treatment with Cy alone or with Cy and normal lymphocytes prolonged survival considerably and cured 20–60% of the mice; mice subjected to Cy in conjunction with in vitro-sensitized lymphoid cells, either syngeneic or allogeneic, had survival rates of 80–100% (100 days). Under the conditions employed, no severe manifestations of clinical graft-versus-host (GVH) reaction were observed. These findings imply that in vitro-sensitized immunocytes and cytoreductive drugs can operate cumulatively.     

Active specific immunotherapy of residual micrometastasis

Summary A vaccine of Bacillus Calmette-Guérin (BCG) admixed with tumor cells induced systemic immunity and had a therapeutic effect on subclinical, disseminated micrometastasis. Inbred strain-2 guinea-pigs given IV injections of 5×10³ to 10⁶ syngeneic L10 hepatocarcinoma cells were vaccinated after metastatic foci were established in the lung parenchyma. The purpose of this study was to establish the variables that can be manipulated to assure optimal immunotherapy while minimizing deleterious side effects of the BCG. In the present study we examined the variables of source, dose, and ratio of BCG to tumor cells. Four BCG sources (lyophilized Tice and Connaught; fresh-frozen Phipps and Tice) were compared. No significant differences among these BCG preparations could be detected with respect to adjuvant potential when they were admixed with attenuated tumor cells in a vaccine. The dose study clearly demonstrated that a BCG dose dependency exists with relation to induction of effective cell-mediated immunity or survival from disseminated micrometastatic disease. Furthermore, evaluations of dose versus ratio of BCG to tumor cells also supported a BCG dose dependency, with the lowest effective BCG dose being directly influenced by tumor burden of the host. Cutaneous reactivity and hypersensitivity of the primary and secondary immunization sites of tumor-bearing animals treated with effective and ineffective vaccines supported the direct association of reaction to BCG and specific tumor immunity. However, when an in vitro leukocyte migration inhibition assay was used, the degree of reactivity to BCG could not be exploited as a quantitative, diagnostic monitor of effective systemic tumor immunity.     

Lack of anti-TSTA antibodies in mice immunized with a methylcholanthrene-induced fibrosarcoma

Summary The 3-methylcholanthrene (MCA)-induced BALB/c (H-2^d) fibrosarcoma C-1 bears a strong tumor-specific transplantation antigen (TSTA) which, in previous studies, appeared to be distinct from H-2^k alien antigens expressed by this tumor. To see whether a syngeneic anti-C-1 serum obtained by multiple immunizations with C-1 tumor cells contained anti-TSTA-specific antibodies, in vitro cytotoxicity tests were performed. The syngeneic anti-C-1 serum had a high cytotoxic activity on C-1 cells, which allowed an absorption analysis to be carried out. Absorption of the serum with C3Hf, AKR, or B10.BR normal lymphoid cells (all sharing H-2^k antigens) reduced the cytotoxic activity on C-1 cells to 30%–50%. This residual activity could not be absorbed by FMR+ or G+ murine leukemias, by ecotropic endogenous virus obtained from SC-1 cells infected with the C-1 virus, by embryonic cells, or by normal BALB/c or C57BL/6 lymphoid cells. Conversely, the serum activity was abrogated by absorbing with the MCA-induced BALB/c fibrosarcomas C-1, ST2, C-3, GI-17, or CMS-1, and significantly lowered by the MCA-induced C3Hf fibrosarcoma C3H-7. A significant reduction of the anti-C-1 cytotoxicity was also obtained by absorbing with the two BALB/c fibrosarcomas teflon-9 and SCS (both lacking TSTA), by means of fresh newborn BALB/c or C3Hf muscle cells or of in vitro-cultured newborn BALB/c fibroblasts. These results suggest that, in spite of the strong transplantation immunity elicited by C-1 cells, antibodies to the individual TSTA of C-1 were undetectable in the syngeneic anti-C-1 serum obtained from animals highly resistant to the challenge of C-1 cells.     

In vitro studies of the rabbit immune system. VI. Rabbit anti-mouse cytotoxic T effector cells are inhibited by anti-rabbit T cell serum in the absence of complement.

Xenogeneic rabbit anti-mouse cell-mediated cytotoxic activity could be generated by culturing lymphoid cells from mesenteric lymph nodes (MLN), spleen, or peripheral blood of rabbits primed 2 to 8 weeks earlier with mouse tumor or spleen cells. MLN cells, which provided the best source of activity after being cultured with 5 to 10 X 10(6) mitomycin C-treated mouse spleen cells for 4 to 6 days, produced 30 to 90% specific isotope release after 4 to 7 hr incubation with 15Cr-labeled tumor target cells. Xenogeneic cytotoxic activity was primarily H-2 specific and could not be blocked by immune complexes but was abrogated by treatment with goat anti-rabbit thymocyte serum plus complement (ATS + C) before or after culture. Therefore, the activity appeared to be mediated by cytotoxic T lymphocytes (CTL). Furthermore, ATS without C abrogated cytotoxic activity when included in the CTL assay at concentrations of 5 to 15 microliter/10(7) effector cells. The inhibitory activity of ATS was directed to the rabbit effector population and could be absorbed completely by rabbit thymocytes. Antisera to mouse T cells with comparable cytolytic activity in the presence of C did not inhibit murine allogeneic CTL.     

Chemo-adoptive immunotherapy against a guinea-pig leukemia

Summary Strain-2 guinea-pigs bearing the transplantable L₂C leukemia were treated with cytoxan 24 h prior to receiving an injection of either allogeneic or syngeneic spleen cells from donors preimmunized to the leukemia. Treatment with the drug alone produced a remission period which lasted for 4–5 weeks before eventual relapse and death. An IP transfer of spleen or peritoneal exudate (PE) cells from syngeneic strain-2 guinea-pigs hyperimmunized to the leukemia greatly extended the survival times of drug-treated animals beyond that observed in animals receiving normal strain-2 cells. Long-term survivors were refractory to a subsequent challenge with a lethal inoculum of L₂C cells. A reduced tumor load was essential for an immunotherapeutic effect of adoptively transferred cells. The use of sensitized lymphocytes alone failed to control the established disease. Hyperimmune spleen cells from strain-13 and Hartley guinea-pigs also demonstrated a slight capacity to inhibit the proliferation of leukemia cells when injected into diseased animals previously treated with the drug. Due to inadequate drug suppression, however, the injection of allogeneic cells from either immune strain-13 or Hartley guinea-pigs did not prolong the latent period for the appearance of the leukemia to the same extent as either immune strain-2 spleen or PE cells. A marked delay in the onset of disease was noted when immune spleen cells from either syngeneic or allogeneic sources were mixed in vitro with L₂C leukemia cells at a ratio of 200:1 before injection back into normal strain-2 animals. However, an exposure of L₂C blast cells in vitro with heat-inactivated serum obtained from L₂C-immune strain-2 animals significantly enhanced the onset of disease.     

Ultrastructural studies of C1300 neuroblastoma cell interaction with syngeneic spleen lymphoid cells.

Sensitized and unsensitized spleen lymphoid cells from A/J mice were induced to form rosettes with cells of clone NB6R of syngeneic C1300 neuroblastoma cells. Light and transmission electron microscopy were applied in combination with ⁵¹Cr release experiments to follow the time course of reaction after rosette formation. With unsensitized lymphoid cells, rosettes formed but target cell morphology in general remained unchanged. With sensitized lymphoid cells a progressive series of morphological changes in the target cells was seen, initially in the mitochondria and, later, when specific ⁵¹Cr release became significant, in the formation of large surface blebs and protrusions. Our data also show another phenomenon occasionally following rosette formation. Lymphocytes were seen within the target cell; these either apparently transformed to lymphoblasts and killed the target cell from the inside or alternatively were destroyed by the host cell and their material was reutilized.     

Natural cell-mediated cytotoxicity in vitro and inhibition of tumor growth in vivo by murine lymphoid cells cultured with T cell growth factor (TCGF)

Summary Lymphoid cells obtained from the spleen, thymus, bone marrow, peripheral blood, and peritoneal exudate of normal mice (BALB/c, BALB/c nude, C57BL/6, C3H) and from spleens of mice bearing a transplantable lung carcinoma or primary mammary carcinoma were expanded in culture for 1–9 months, with an increase in cell number of 10⁵- to 10⁶-fold per month, in crude or lectin-depleted medium containing T cell growth factor (TCGF). All these cultured lymphoid cell (CLC) lines exhibited strong cytotoxic activity in vitro (assessed by ⁵¹Cr-release assays) toward a variety of freshly harvested and cultured syngeneic, allogeneic, and xenogeneic tumor target cells, both lymphoid and solid (including metastatic growths) in origin. Extensive killing was observed against tumor targets that were resistant to lysis by natural killer (NK) cells as well as to NK-sensitive tumor lines. Low levels of cytotoxic reactivity were also demonstrated against fresh and cultured normal lymphoid cells. The CLC had some characteristics of NK cells but also expressed some typical T cell markers. In local Winn-type neutralization assays, CLC delayed or completely inhibited the growth of lymphomas and carcinomas in syngeneic and allogeneic recipients. In mice with metastatic growth of a second-generation transplant of mammary carcinoma, CLC were shown to have some therapeutic effect when administered IV 1 day after cyclophosphamide. No significant beneficial action of IV administered CLC was observed in the absence of chemotherapy in mice implanted with a lung carcinoma. The possibilities of employing TCGF-propagated cytotoxic effector cells in adoptive immunotherapy of human malignancies are discussed.     

Cell cooperation in abolition of tolerance of xenogeneic tumor.

Thymectomized, lethally irradiated mice reconstituted with syngeneic bone marrow cells are tolerant to xenogeneic Yoshida ascites sarcoma (YAS). The tolerance was abolished by an injection of syngeneic normal spleen, thymus, or lymph node cells given simultaneously with YAS. Allogeneic and semiallogeneic spleen cells were ineffective. The YAS-rejecting mice produced specific anti-tumor antibodies. The serum of these mice transferred to tolerant T-cell-deficient mice protected the latter from inoculated YAS cells. These serum-protected mice were not able to resist the reinoculum of the tumor cells as the mice restored with lymphoid cells did. The latter mice rejected the YAS at the time when donor cells were practically absent in their lymphoid tissue. The low effective ratio of injected syngeneic lymphoid to tumor cells, efficiency of injected thymus cells, and other data led to the conclusion that transferred lymphoid cells did not act directly on tumor cells but through cooperation with host lymphoid cells. The cooperation of donor T- and host B-lymphocytes enabled the activation of the latter, and YAS cells were rejected.     

Immunogenicity of subcellular fractions and molecular species of MuLV-induced tumors

Summary YBA, a Moloney virus-induced leukemia in CBA mice, and a relatively weak immunogenic tumor, was screened for the presence of immunogenic antigens. The tumor was subjected to homogenization and subcellular fractionation on sucrose gradients; the immunogenic subcellular fractions underwent further separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The immunogenicity of the subcellular fractions and the SDS-PAGE-isolated molecular species were tested by (their) subcutaneous injection into syngeneic mice and examination of their splenocytes examined against tumor cell and normal cell targets by the chromium release cell-mediated lympholysis assay. Tumor cell homogenates were also separated by SDS-PAGE and tested for immunogenicity without prior fractionation.Splenocytes from mice that had received injections of certain SDS-PAGE-isolated epitopes derived from YBA tumor homogenate or its light and heavy subcellular fractions generated effective cytotoxic responses against YBA target cells after 6 days in vitro cultivation. In contrast, intact YBA tumor cells or non-separated tumor homogenates failed to induce an efficient cytotoxic response. The effector cells induced with the immunogenic SDS-PAGE-isolated epitopes of YBA tumor were specific, since they cytolysed the homologous target cells more efficiently than unrelated target cells or syngeneic normal cells. The activity of these effector cells was affected by varying the effector : target ratio. Augmentation of the cytotoxic responses was obtained when the splenocytes of mice immunized with SDS-PAGE-isolated epitopes of YBA tumor were restimulated in vitro, with the homologous neoplastic cells.Immunogenic SDS-PAGE epitopes were isolated from YAC tumor also (YAC is a Moloney-induced tumor of A mice). The effector cells induced with these separated epitopes were characterized as thymus-derived cells and not as natural killer cells.The results suggest that (1) the molecular repertoire of YBA and YBA tumors contain immunogens that can induce a specific antitumor cell-mediated response; (2) the isolated molecular species injected are more efficient immunogens than the entire, unseparated homogenate sample or a dose of 10⁸ intact inactivated tumor cells; and (3) the gel matrix may be responsible for the enhanced cell-mediated response induced against the weakly immunogenic tumor.     

Suppression of the guinea-pig line-10 hepatocarcinoma by a factor(s) released from line-10 cells

Summary A factor or factors released from line-10 hepatocarcinoma cells during mixing in a fluid medium suppressed tumor growth when injected intradermally (ID) with viable line-10 cells to strain-2 guinea-pigs. No suppressive factor was released from other syngeneic normal adult, fetal, or tumor cells. The mechanism behind the tumor suppression was not determined, although antigens derived from line-10 cells were demonstrated in media containing the suppressive factor(s).     

Inability of choleragenoid-sensitized cells to induce T cell-mediated cytolysis.

Murine splenocytes and tumor cells bind cholera enterotoxoid (choleragenoid). Four hours after sensitization, choleragenoid-coated cells were lysed in the presence of anti-cholergenoid serum and complement, indicating that the binding was stable. Choleragenoid-coated cells were unable to sensitize spleen cells from normal or choleragenoid primed syngeneic mice into displaying a cytotoxic effect against choleragenoid-coated target cells in the T cell-mediated cytotoxicity assay. Cells coated with both choleragenoid and trinitrophenyl (TNP) groups did sensitize syngeneic spleen cells to display a cytotoxic effect against target cells bearing choleragenoid and TNP or TNP alone, but not choleragenoid alone. These data demonstrate that the mere binding of a foreign component to lymphoid cells is not sufficient to allow sensitization of cytotoxic T cells.