The impact of fetal sex on pregnancy and neonatal outcomes in twin gestation.

PURPOSE: Fetal sex is independently associated with pregnancy complications and impacts neonatal outcomes. Evidence suggests that females have an advantage over males, with a better outcome in the perinatal period. In addition, fetal outcome in twin gestations is also related to the intrauterine position of the fetus, such as the first, the presenting or second twin. It has been demonstrated that the neonatal outcome of the second fetus is worse than that of the first fetus. This study aimed to examine the influence of fetal sex on obstetric outcomes in twin pregnancies based on the location of the fetus in the uterus. METHODS: Retrospective study. Maternal and obstetric outcomes were compared among three groups: male‒male, female‒female, and male‒female groups. Comparisons of neonatal outcomes were performed among the four groups: male A-male B, male A-female B, female A-male B, and female A-female B. RESULTS: A total of 1073 twin gestations were included, comprising 288 male‒male, 288 female‒female, and 497 male‒female gestations. A greater percentage of neonates admitted to the NICU was observed for male fetuses than for female fetuses. Adverse composite neonatal outcome was more common in the male‒male group than in the female‒male group and in the female‒female group. CONCLUSION: Twin gestation with a first twin male tends to have worse neonatal outcomes than does twin gestation with a first twin female. The presence of a male co-twin increases the risk of adverse outcomes.

[Neuropsychological and MRI diagnostics in secondary progressive multiple sclerosis]. / Neuropsychologische und Magnetresonanztomographie(MRT)-Diagnostik bei sekundär progredienter Multipler Sklerose.

BACKGROUND: Multiple sclerosis is a disease continuum with an initial relapsing remitting course (RRMS) and secondary progression (SPMS) at later stages. Most of the hitherto approved treatments do not adequately control for the phase of secondary progression. Thus, early detection of SPMS conversion is a key issue to initiate SPMS-tailored treatment. In this context, assessment of cognitive functions and magnetic resonance imaging (MRI) both play an important role in the longitudinal follow-up of MS patients. OBJECTIVE: To elucidate the importance of cognitive testing and MRI for prediction and detection of SPMS conversion as well as to discuss strategies for disease monitoring and for optimizing treatment in standard clinical care, particularly in outpatient settings. MATERIAL AND METHODS: Review article based on a nonsystematic literature review. RESULTS: Standardized cognitive testing can support early diagnosis of SPMS and facilitate disease monitoring. Annual application of sensitive screening tests, such as the Symbol Digit Modalities Test (SDMT) and Brief Visual Memory Test-Revised (BVMT­R) or the entire Brief International Cognitive Assessment for MS (BICAMS) test battery are recommended in this context. The MRI evidence of persistent inflammatory activity within 3 years of diagnosis as well as evidence of cortical lesions are predictive for SPMS conversion. Standardized MRI monitoring for markers of progression can substantiate clinical and neurocognitive signs of SPMS conversion. CONCLUSION: Multidisciplinary patient care involving careful clinical examination, neuropsychological testing and MRI monitoring is of great significance for the prediction of SPMS conversion and diagnostics. This enables early treatment adaptation, since pharmacological interventions in SPMS differ from those in RRMS. Continuous clinical, neuropsychological and MRI vigilance enable stringent monitoring of treatment outcomes with respect to neuroinflammatory and neurodegenerative activity as well as treatment-related complications.

Baseline predictors of persistence to first disease-modifying treatment in multiple sclerosis.

OBJECTIVES: Patients with multiple sclerosis (MS) require lifelong therapy. However, success of disease-modifying therapies is dependent on patients' persistence and adherence to treatment schedules. In the setting of a large multicenter observational study, we aimed at assessing multiple parameters for their predictive power with respect to discontinuation of therapy. MATERIALS AND METHODS: We analyzed 13 parameters to predict discontinuation of interferon beta-1b treatment during a 2-year follow-up period based on data from 395 patients with MS who were treatment-naïve at study onset. Besides clinical characteristics, patient-related psychosocial outcomes were assessed as well. RESULTS: Among patients without clinically relevant fatigue, males showed a higher persistence rate than females (80.3% vs 64.7%). Clinically relevant fatigue scores decreased the persistence rate in men and especially in women (71.4% and 51.2%). Besides gender and fatigue, univariable and multivariable analyses revealed further factors associated with interferon beta-1b therapy discontinuation, namely lower quality of life, depressiveness, and higher relapse rate before therapy initiation, while higher education, living without a partner, and higher age improved persistence. CONCLUSIONS: Patients with higher grades of fatigue and depressiveness are at higher risk to prematurely discontinue MS treatment; especially, women suffering from fatigue have an increased discontinuation rate.

Drug-resistant MS spasticity treatment with Sativex(®) add-on and driving ability.

OBJECTIVE: The aim of the present observational study was to determine the effects of a delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) oromucosal spray (Sativex(®) spray), brand name Sativex(®), indicated for drug-resistant MS spasticity, on the driving ability of treated MS patients. METHODS: The study was conducted over a period of 4-6 weeks. Thirty-three MS patients with moderate to severe treatment-resistant spasticity and planned to begin add-on treatment with Sativex(®) were enrolled at three specialized MS centres in Germany. A set of five driving test procedures from a validated computerized test battery was used to evaluate the driving ability of eligible patients. Tests were performed by patients at baseline and repeated after 4-6 weeks of treatment with Sativex(®) oromucosal spray. According to German normative data, the test thresholds achieved by the general population served as a reference to allow for a fitness/unfitness to drive classification. RESULTS: Patients showed comparable driving test results at baseline and at final visits. Only two patients changed classification shifting from 'unfit' to drive to 'fit' and vice versa. The mean severity of spasticity, as self-reported by the patients, improved with statistical significance. Sativex(®) was generally well tolerated. CONCLUSIONS: Treatment of MS patients with Sativex(®) does not negatively impact on driving ability and may improve moderate to severe treatment-resistant MS spasticity.

Design of T-cell receptor libraries with diverse binding properties to examine adoptive T-cell responses.

Adoptive T-cell therapies have shown significant promise in the treatment of cancer and viral diseases. One approach, which introduces antigen-specific T-cell receptors (TCRs) into ex vivo activated T cells, is designed to overcome central tolerance mechanisms that prevent responses by endogenous T-cell repertoires. Studies have suggested that use of higher-affinity TCRs against class I major histocompatibility complex antigens could drive the activity of both CD4(+) and CD8(+) T cells, but the rules that govern the TCR binding optimal for in vivo activity are unknown. Here, we describe a high-throughput platform of 'reverse biochemistry' whereby a library of TCRs with a wide range of binding properties to the same antigen is introduced into T cells and adoptively transferred into mice with antigen-positive tumors. Extraction of RNA from tumor-infiltrating lymphocytes (TILs) or lymphoid organs allowed high-throughput sequencing to determine which TCRs were selected in vivo. The results showed that CD8(+) T cells expressing the highest-affinity TCR variants were deleted in both the TIL population and in peripheral lymphoid tissues. In contrast, these same high-affinity TCR variants were preferentially expressed within CD4(+) T cells in the tumor, suggesting they had a role in antigen-specific tumor control. The findings thus revealed that the affinity of the transduced TCRs controlled the survival and tumor infiltration of the transferred T cells. Accordingly, the TCR library strategy enables rapid assessment of TCR-binding properties that promote peripheral T-cell survival and tumor elimination.

Single-chain VαVß T-cell receptors function without mispairing with endogenous TCR chains.

Transduction of exogenous T-cell receptor (TCR) genes into patients' activated peripheral blood T cells is a potent strategy to generate large numbers of specific T cells for adoptive therapy of cancer and viral diseases. However, the remarkable clinical promise of this powerful approach is still being overshadowed by a serious potential consequence: mispairing of the exogenous TCR chains with endogenous TCR chains. These 'mixed' heterodimers can generate new specificities that result in graft-versus-host reactions. Engineering TCR constant regions of the exogenous chains with a cysteine promotes proper pairing and reduces the mispairing, but, as we show here, does not eliminate the formation of mixed heterodimers. By contrast, deletion of the constant regions, through use of a stabilized Vα/Vß single-chain TCR (scTv), avoided mispairing completely. By linking a high-affinity scTv to intracellular signaling domains, such as Lck and CD28, the scTv was capable of activating functional T-cell responses in the absence of either the CD3 subunits or the co-receptors, and circumvented mispairing with endogenous TCRs. Such transduced T cells can respond to the targeted antigen independent of CD3 subunits via the introduced scTv, without the transduced T cells acquiring any new undefined and potentially dangerous specificities.

Selection of macrophage-resistant progressor tumor variants by the normal host. Requirement for concomitant T cell-mediated immunity.

The ultraviolet radiation-induced fibrosarcoma 1591 is generally rejected by normal syngeneic mice, but occasionally the tumor succeeds in growing progressively. Analysis of these progressively growing tumors has regularly demonstrated the development of tumor variants that have acquired a heritable progressive growth potential. We have analyzed the phenotypic changes of these variants to determine which kind of selection pressure had occurred during the evolution of the variants, thus giving insight into the relative importance and hierarchy of the different immune defense mechanisms that may be operating in normal individuals as a defense against neoplastic cells. We discovered that all of the host-selected progressor variants had lost not only a strong T cell-recognized and tumor-specific antigen, but also their high sensitivity to cytotoxic macrophages. No selection for macrophage-resistance or loss of the tumor antigen was observed in 1591 tumors reisolated from idiotypically-suppressed mice or from other mice lacking tumor-specific T cell immunity. Analysis of other tumor variants selected in vitro showed that 1591 tumor cells have the potential to lose sensitivity to tumoricidal macrophages without losing the T cell-recognized tumor antigen. Thus the data suggest that T cells and macrophages act together to suppress the outgrowth of potentially malignant cells in vivo.

Tumor necrosis factor/cachectin. Induction of hemorrhagic necrosis in normal tissue requires the fifth component of complement (C5).

TNF induces hemorrhagic necrosis (HN) when injected into skin exposed to bacterial agents but not when injected into normal skin. In this paper, we present several lines of evidence suggesting that TNF requires the fifth component of complement (C5) to induce HN in skin exposed to bacteria. First, mouse strains that do not have C5 did not develop HN after injection of TNF and bacteria into skin. Second, plasma from C5-sufficient mice could correct the defect in these C5-deficient mice. Third, heating at 56 degrees C for 30 min inactivated the capacity of plasma to reconstitute C5-deficient mice. Fourth, CVF, which is known to inactivate complement, abrogated the capability of C5-sufficient mice to respond. Fifth, depleting plasma of hemolytic activity while generating C5a did not affect the capacity of the activated plasma to reconstitute C5-deficient mice. Finally, only the plasma fraction containing molecules of the size range of C5a reconstituted C5-deficient mice. These findings indicate that C5a and not the membrane attack complex is required for HN. Although we do not know through which mechanism C5a participates in the development of HN, we propose that the described HN response is related to a local defense mechanism in which TNF and C5a lead to the disruption of capillaries in the direct vicinity of bacteria. By this mechanism the rapid spread of bacteria or their products into the circulation is prevented. Such a tissue response is consistent with the known higher susceptibility of C5-deficient mice to bacterial infections and provides a model with which to search for the multiple steps involved in this important local defense mechanism.

A tumor escape variant that has lost one major histocompatibility complex class I restriction element induces specific CD8+ T cells to an antigen that no longer serves as a target.

After loss of expression of a major histocompatibility complex class I Kk allele, the escape variant of an immunogenic tumor grows progressively in normal mice. This progressor variant is resistant to killing by cytotoxic T lymphocytes (CTLs) directed against the A and B antigens presented by Kk. Although the variant retains the expression of the Dk allele and is sensitive to CTLs directed against the C antigen presented by Dk, the variant failed to induce CTLs to this antigen in vivo. Instead, the variant induced CD8+ T cells directed to the A antigen. This was shown at the molecular level by T cell receptor beta chain sequence analysis of the responding cells. Further evidence for the presence of A antigen in the variant came from the finding that spleen cells of mice injected intraperitoneally with the variant tumor cells were primed for an anti-A CD8+ CTL response in vivo. Thus, in contrast to other variants that lost a target antigen and induced a CTL response to remaining target antigens, the Kk loss variant continued to induce an immune response to a tumor antigen that is no longer presented on the tumor cell surface. Even though the variant escapes in a single step because an effective CTL response to secondary antigens is prevented, these secondary antigens remain as potential targets of immunotherapy on the variant's cell surface.

Inhibition of tumor growth by elimination of granulocytes.

As observed for many types of cancers, heritable variants of ultraviolet light-induced tumors often grow more aggressively than the parental tumors. The aggressive growth of some variants is due to the loss of a T cell-recognized tumor-specific antigen; however, other variants retain such antigens. We have analyzed an antigen retention variant and found that the variant tumor cells grow at the same rate as the parental tumor cells in vitro, but grew more rapidly than the parental cells in the T cell-deficient host. The growth of the variant cells was stimulated in vitro by factors released from tumor-induced leukocytes and by several defined growth factors. In addition, the variant cancer cells actually attracted more leukocytes in vitro than the parental cells. Furthermore, elimination of granulocytes in vivo in nude mice by a specific antigranulocyte antibody inhibited the growth of the variant cancer, indicating that this tumor requires granulocytes for rapid growth.

Immunoselection of tumor cell variants by mice suppressed with ultraviolet radiation.

It has previously been shown that mice exposed to ultraviolet radiation (UV) fail to reject highly immunogenic UV-induced tumors, which are regularly rejected by normal mice. The present study shows, however, that this immunosuppresion is incomplete, as UV-treated mice can still mount certain tumor-specific immune responses and reject smaller inocula of tumor cells that regularly grow progressively in athymic nude mice. Furthermore, all tumor cell lines that were reisolated from the tumor mass resulting from one tumor passage through UV-treated recipients heritably lost a tumor-specific determinant present on the parental tumor cells used for transplantation, and a large percentage of these reisolated variant tumors had changed to progressively growing tumors, in that they were no longer rejected by normal mice. In contrast, none of the tumors reisolated from passage through athymic nude mice or anti-idiotypically suppressed mice showed this change in antigenicity and progressive growth behavior. Thus, it appears that the phenotypic change in tumors reisolated from UV-treated mice was caused by immunoselection, and that the tumor-specific immunity in these mice apparently restrained the outgrowth of the parental tumor cells despite the partial immunosuppression. Because of the regularity at which tumor variants arose in the UV-treated mice after tumor transplantation, it appears that the partial immunosuppression caused by UV-treatment may have favored the outgrowth of antigenic variants from the parental tumor cell population, possibly by allowing more time for the generation of tumor variants. A similar immunoselection process might be part of tumor progression during tumor development and preferentially occur in cancer-bearing individuals showing concomitant tumor immunity.

Loss of tumor-specific and idiotype-specific immunity with age.

The ultraviolet light-induced fibrosarcoma 1591 undergoes "first-set rejection" when transplanted into normal syngeneic mice. We found, however, that the primary resistance of normal mice decreases with age, beginning at 9--12 mo, equivalent to middle age for mice. Mice lose with age the capacity to mount both idiotypic and anti-idiotypic responses responsible for controlling the growth of tumor. This loss was correlated with quantitative as well as qualitative changes in the response, such as changes in specificity and clonotype. Normal young mice regularly expressed a dominant common anti-1591 "idiotype" as defined by an anti-idiotypic probe. The capability of normal mice to respond with lymphocytes of this dominant common idiotype began to decline at about 8 mo of age. At this time, animals still generated tumor-specific lymphocytes, but these lymphocytes appear to be idiotypically different lymphocyte clones. With further increase in age, animals responded with tumor-reactive lymphocytes that showed a marked cross-reactivity to other tumor target cell lines. Both in vivo and in vitro, the capability of normal mice to mount an immune response that was specific for the 1591 tumor cells decreased between 9 and 14 mo, which was the age individual mice became increasingly susceptible to a challenge with 1591 tumor cells. Thus, our data suggest that clones of tumor-specific T cells provide primary and early protection of young animals against challenge with malignant 1591 cells. However, the dominance of these tumor-specific T cell clones in a primary immune response is lost in middle-age. Because the ability of animals to mount anti-idiotypic immune response also declined in middle-aged animals, it is possible that the observed loss of clonal dominance of tumor-specific clones with increasing age is at least partially related to age-dependent changes in the anti-idiotypic compartment.

Tumor antigens defined by cloned immunological probes are highly polymorphic and are not detected on autologous normal cells.

We have isolated UV light-induced and spontaneous tumors along with nonmalignant cells and tissues from each host. CD8+ CTL clones generated to a number of highly immunogenic UV-induced tumors did not react with autologous normal fibroblasts nor with autologous second tumors. Using up to 25 independently induced tumors as targets, these CTL clones were found to be uniquely specific for the particular tumor used for immunization even when multiple tumors isolated from the same animals were used as targets. In addition to this extensive antigenic diversity of independently induced tumors, we found that a single cancer cell can express multiple independent antigens that were uniquely expressed on the tumor but were not detectable on autologous nonmalignant fibroblasts. A poorly immunogenic spontaneous tumor was also found to express an antigen that was uniquely specific for the immunizing tumor in that it was absent from any of 25 other tumors tested. This antigen was recognized by a mAb and not detected on autologous nonmalignant fibroblasts or on an autologous second spontaneous tumor. These findings demonstrate that syngeneic CTL clones or mAbs can define unique antigens on UV-induced or spontaneous tumors. The use of autologous nonmalignant fibroblast targets made it unlikely that these antigens were widely expressed on normal cells. The availability of cloned immunological probes to antigens on tumors isolated with autologous normal cells will allow a reliable identification of the genetic origins of unique antigens on experimentally induced and spontaneous tumors and permit a decisive answer to whether these unique antigens are encoded by normal genes or by genes that have undergone somatic mutations; i.e., whether these antigens are truly tumor specific.

Identification of a unique tumor antigen as rejection antigen by molecular cloning and gene transfer.

Tumor-specific transplantation antigens are antigens that can lead to complete immunological destruction of a transplanted cancer by the syngeneic host. When such antigens are expressed on cancers induced by chemical or physical carcinogens, then they are usually unique, i.e., antigenically different for each independently induced tumor. In this study, we show that the product of a gene encoding a novel MHC class I molecule and isolated from the murine UV light-induced regressor tumor 1591 represents one such unique tumor-specific transplantation antigen that causes tumor rejection. The major evidence comes from our finding that 1591 progressor variants regularly lost the gene encoding this antigen that is expressed in the parental tumor that regresses in normal mice; furthermore, reintroduction of this gene into a 1591 progressor variant by DNA transfection caused the progressor variant to regress in normal immunocompetent mice. Thus, the progressor tumor reverted to the parental regressor phenotype following transfection. Consistent with the conclusion that the expression of the novel MHC class I gene following transfection was responsible for the regressor phenotype is also our finding that a variant of the transfected tumor that had lost expression of the transfected gene resumed its progressive growth behavior. Finally, we show that the molecule encoded by the novel class I gene is specifically recognized by a syngeneic tumor-specific cytolytic T cell clone that we have previously shown to select in vitro for progressor variants from the parental regressor tumor cell line. It remains to be determined to what extent unique tumor-specific rejection antigens of other highly immunogenic regressor tumors are encoded by novel MHC class I genes and whether these genes represent germline mutations or somatic mutations caused by the carcinogen treatment.

Stroma is critical for preventing or permitting immunological destruction of antigenic cancer cells.

Inoculated immunogenic cancer cells after initial growth are potentially rejected by specific host immunity; however, the outcome of the interaction between host and inoculated cancer cells is a function of multiple factors including the route of inoculation, the number of cells, the density of antigens on the injected cancer cells, and the state of the immune system of the host. In the present study, we have examined a different kind of variable: the stroma that inoculated tumor cells initially reside in. The impetus to examine this factor arises from observations that cancer cells from several lines inoculated as fragments of solid tumors often grow progressively, whereas the same number or more than 10-fold larger numbers of identical type cells injected as a suspension are rejected, even though fragments or suspended cells are both tumorigenic at the same doses in nude mice. In the present studies, we found that: (a) indeed, cancer cells inoculated as fragments were more tumorigenic than cancer cells in suspension; (b) the tumorigenicity of suspended cancer cells was increased by injection of the cells into polyurethane sponge implants; (c) cancer cells were more tumorigenic embedded in syngeneic stroma than in transgenic antigenic stroma expressing the K216 major histocompatibility complex class I antigen; and (d) antigenic, bone marrow-derived, stromal components (presumably passenger leukocytes) were sufficient to cause rejection of immunogenic but antigenically unrelated cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression by autogenous complementary idiotypes: the priority of the first response.

Complementary idiotypes or antibodies are considered to have combining site structures which are at least partly directed against each other. Complementary antibodies were induced in A/He mice by immunization with phosphorylcholine (PC)-containing antigens and by immunization with the PC-binding IgA myeloma protein TEPC-15 (T15). Both responses were monitored by enumerating plaque-forming cells (PFC) and assaying serum antibody levels against the corresponding antigens. Mice immunized at least three times with T15 in adjuvants had markedly suppressed responses to subsequent immunization with PC; similarly, mice preimmunized multiple times with PC had suppressed responses to immunizations with T15. In contrast, mice immunized with T15 in the interval between "primary" and "secondary" immunizations with PC had undiminished PFC responses to both antigens but significantly decreased antibody titers to PC. Simultaneous responses were also induced by immunizations with T15 superimposed on weekly immunizations with PC; with this regime, immunization with T15 actually enhanced the PFC response to PC, but serum antibody to PC was significantly lower than for mice immunized with PC only. Levels of serum antibody to PC were probably lower, either because anti-PC antibody was complexed with the complementary antibody directed against T15, or because the antibody directed against T15 prevented synthesis and/or release of anti-PC antibody by cells in vivo. Thus, an established prior autogenous immune response can dramatically suppress a subsequent primary complementary response, but the effects of complementary responses on each other are more complex with different sequences of immunization. Also, the effects of variables such as the amounts and ratios of the classes of antibodies on regulation of complementary responses remain to be defined.

Mechanisms of syngeneic tumor rejection. Susceptibility of host-selected progressor variants to various immunological effector cells.

The ultraviolet radiation-induced fibrosarcoma 1591 generally is rejected by normal syngeneic mice and only rarely exhibits progressive growth. We isolated five of these rare progressor tumors from normal animals to determine the selective pressures that had been exerted upon the parental tumor by normal immunocompetent hosts. We found that the variant tumor cell lines could neither induce nor be killed by tumor-specific lymphocytes, suggesting that selection had been exerted against tumor cells expressing the tumor-specific antigen. In contrast, no selection against natural killer cell activity or against nonspecific T cell-mediated immunity seems to have occurred because progressor tumor cells were highly sensitive to these types of effector cells and in fact induced these effector cells more effectively than did the parental tumor. Nude mice were found to be as capable as normal mice in generating natural killer activity in response to a challenge with progressor tumor cells, but they were unable to mount a nonspecific T lymphocyte response. This may account for the fact that the progressor tumors grew at a significantly faster rate in nude animals than in normal mice. Thus, our study shows that in this tumor system nonspecific T cell-mediated immunity may play a role in retarding tumor growth, but the absolute resistance of normal animals to progressive tumor growth critically depends upon the presence of T cell-mediated tumor-specific immunity. Furthermore, neither NK cells nor nonspecific cytotoxic T lymphocytes appear to play a role in immunoselection against this tumor in normal immunocompetent hosts.

Animals bearing malignant grafts reject normal grafts that express through gene transfer the same antigen.

Breaking the state of immunological unresponsiveness of tumor-bearing individuals to cancer is a prerequisite for active or passive tumor-specific immunotherapy. To study this problem the immunogenic MHC class I antigen, K216 was transfected into a progressor tumor. The transfected tumors were regularly rejected by normal mice but grew progressively in mice bearing nontransfected tumors. In addition, transgenic mice were derived to obtain normal cells and tissues expressing the same K216 gene product. Normal mice rejected K216-positive normal or malignant tissue grafts and generated K216-specific CTL in vitro and in vivo in response to these challenges. In contrast, mice bearing nontransfected tumors, though rejecting K216-positive nonmalignant tissue grafts, did not reject K216-positive tumors nor generate K216-specific CTL in response to K216-positive tumor cells. Mice bearing K216-positive tumors also rejected the nonmalignant K216-positive tissue grafts, but this in vivo response failed to lead to rejection of the simultaneously present tumor graft expressing the same antigen; in fact, immunity had no measurable effect whatsoever on tumor size or incidence and caused no selection for antigen loss variants. Taken together, the present findings suggest that transfer of expression of a target antigen into nonmalignant cells provides a way for obtaining effective stimulation of antigen-specific CTL in tumor-bearing mice, but that additional manipulations will be required to cause immunological rejection of established tumors.

Multiple cancers. Tumor burden permits the outgrowth of other cancers.

We demonstrate that tumor-bearing hosts permit the outgrowth of "potentially malignant" cells that are located at a different site. These second cancers continued to grow and kill their hosts even though they retain the "premalignant" phenotype, even after removal of the original malignancy. The potentially malignant cells used in these experiments were ultraviolet light- or methylcholanthrene-induced regressor tumor cells that are rejected regularly by normal mice at any testable dose, and only form progressive tumors in immunosuppressed individuals. The immunological rejection of these highly immunogenic, potentially malignant cells was suppressed by Thy-1+, Ly-2-, nonadherent, radio-sensitive suppressor cells in the tumor-bearing mice. These suppressor cells were absent in nude tumor-bearing mice. Unlike helper and cytolytic T cell-mediated responses, which are exquisitely tumor specific, the suppression caused by a progressively growing tumor was crossreactive among many syngeneic, independently derived tumors induced by different carcinogens. However, T cell-mediated immune responses to alloantigens, allogeneic tumors, certain syngeneic tumors, and humoral responses to xenogeneic red blood cells were normal in these mice. The immune suppression in the tumor-bearing animals closely simulated that induced by ultraviolet light irradiation, and both types of suppression might therefore share common mechanisms. Our findings may contribute to understanding the growth, development, and possible control of multicentric malignancies and add a precaution to the potential use of strongly immunogenic tumor variants for active immunotherapy in hosts bearing less immunogenic tumors.

Highly malignant tumor variants retain tumor-specific antigens recognized by T helper cells.

We have studied the components of a complex of tumor-specific antigens to determine if all of the components of the complex were lost during progression from a rather benign regressor tumor to a highly malignant (HM) cancer. We find that the HM tumor cells have lost antigens recognized by CTL but retained antigens recognized by Th cells. Immunization with variants expressing Th-defined antigens induced tumor-specific immunity to challenge with a parental variant that expressed a CTL-recognized target antigen, but did not induce immunity to challenge with the variant that expressed the Th-defined antigen alone. Together, these findings suggested that Th cells fail to exert direct selective pressure upon the tumor, resulting in retention of "lineage-specific," Th-recognized antigens by highly immunoselected variants. Possible advantage could be taken of this fact for the development of specific immunotherapy.