Cancer vaccines: the perspective of the Cancer Immunology Branch, NCI.

The Cancer Immunology Branch, NCI, is supporting a great deal of exciting research relevant to cancer vaccine development. The few areas highlighted here are representative of ongoing research opportunities, but further progress depends largely on a continued infusion of investigator-initiated ideas to realize the potential of current research areas and open new ones.

Cancer immunology: highlights of the NCI Extramural Immunology Program.

The long-term goal of research supported by the Immunology Program is to better understand immune mechanisms and their regulation in order to develop more effective strategies to strengthen the immune response against cancer. While there has been much progress in the field of immunology in recent years, many major questions remain unanswered. The role of MHC antigens in regulating the immune response to tumors is still unclear, as is the nature of putative tumor-associated antigens which are the targets of this response. The efficacy of various immune cell subsets in tumor cell killing is differentially affected by changes in tumor cell surface MHC antigen expression. Furthermore, although we now know much more about the cellular interactions in the immune response, little is actually known about the particular cell subsets which participate in an immune response is regressing versus progressing tumors. Interleukins have been shown to stimulate a variety of immunes response, and some of these immune modulators are now being tested in clinical trials, in various stages, to determine their antitumor effects. However, systemic administration of large quantities of interleukins can result in very different effects than those created by the local release of effector molecules from specific T-cell populations. Effector T cells can deliver lymphokines to precise target structures, whereas systemically administered lymphokines would affect preferentially those cells expressing the largest numbers of high affinity receptors for the lymphokines. The specificity of lymphokines as mediators of immunologic response rests largely or exclusively in the local release of such materials by T cells upon activation by antigen: MHC complexes on a stimulating cell. Because lymphokines show specificity only for nonantigen-specific, non-MHC-restricted receptor molecules on target cells, the effect of lymphokine injections is likely to be determined solely by the expression of these receptors. Thus, lymphokines function well as effector molecules in a number of specific immune reactions, but it remains to be determined whether they will be useful in regulating immune responses in specific disease situations. It may be critical to recruit specific immune cells to the area of tumor growth where they, in turn, can release lymphokines to activate appropriate antitumor effector cells. Adoptively transferred T cells of the helper phenotype can induce an effective antitumor immune response in recipient mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetics of immunoglobulin and specific antibody responses of CBA mice infected with Trypanosoma rhodesiense.

Groups of CBA/CaJ and B-cell deficient CBA/N mice were infected with Trypanosoma rhodesiense EATRO 1886 strain. Survival, parasitaemia, serum Ig levels plus specific trypanosomal IgM and IgG antibodies were assayed and compared during infection. Whereas both strains of mice had similar parasitaemias during the first week of infection, CBA/N parasitaemias were lower than those observed in CBA/CaJ mice during the subsequent study period. Antibody responses, specific for T. rhodesience antigens, peaked on day 10 after infection in CBA/CaJ mice, then rapidly declined. However, antibody responses in CBA/N mice remained elevated throughout the study. In addition, the kinetics of specific IgG and IgM varied in CBA/N mice: IgG antibody was detected on day 4, whereas specific IgM was detected on day 16. This unique relationship between the appearance of IgG and IgM antibody may explain the longer survival observed for B-cell deficient CBA/N mice infected with T. rhodesience.

Induction of T cell activity in athymic (nu/nu) mice infected with Trypanosoma rhodesiense.

Infection of C57BL/10 (B10)3 nu/nu mice with Trypanosoma rhodesiense results in the development of significant T-cell reactivity in spleen and lymph nodes. The proliferative responses to mitogens, such as concanavalin A (Con A) and phytohemagglutinin (PHA), and in mixed-lymphocyte reactions (MLR) to alloantigens are enhanced compared with control uninfected nu/nu mice. These results serve to emphasize the stimulatory nature of trypanosomes on the immune system.

Iodination and identification of surface membrane antigens in procyclic Trypanosoma rhodesiense.

Surface membrane proteins and glycoproteins of procyclic Trypanosoma rhodesiense were labeled with 125I by the use of the insoluble catalyst Iodo-Gen. Autoradiography of whole solubilized procyclic trypanosomes after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed a minimum of 25 surface components to have incorporated radioactivity. These components ranged in m.w. from approximately 10,000 to approximately 285,000. Immunoprecipitation with rabbit antisera of Triton X-100 extracts of radiolabeled trypanosomes revealed a subset of at least 14 surface antigens. Two of these antigens (m.w. of 63,000 and 96,000) showed heavy incorporation of label and may be major proteins of the procyclic membrane. Sera from trypanosome-infected mice recognized an overlapping but different subset of surface antigens, including a doublet of very high m.w. Lectin precipitation using antilectin conjugates or bead-bound lectins indicated that many of the labeled surface components are glycoproteins including the two major proteins precipitated by rabbit antisera. Radiolabeled glycoproteins identified by these methods bear alpha-methyl-mannopyranoside and/or galactose residues but not N-acetyl glucosamine or fucose residues in quantity. The use of these methods in identifying potentially pathogenic trypanosomal antigens is suggested.

Survival of mice injected with Plasmodium vinckei or Plasmodium yoelii XL by the footpad route.

NIH-white mice were injected with varying doses of Plasmodium vinckei or Plasmodium yoelii lethal via the hind footpad (FP), intraperitoneal (IP), subcutaneous (SC) routes. Survival was dependent on the dose of the inoculum and route of injection. Injection via the IP and SC routes led to higher mortality than the FP route. The results showed that at a dose of 10 4 parasitized erythrocytes injected IP led to 100% mortality, whereas the same dose injected via the FP route gave protection.

Non-specific immune responses in CBA/N mice infected with Trypanosoma brucei.

CBA/N mice carry a genetic defect which causes a maturational arrest of normal B lymphocyte development, and results in an inability to mount IgM antibody responses against certain T lymphocyte-independent antigens. These mice were found to survive an experimental infection with Trypanosoma brucei two to three times longer than conventional mice. This enhanced survival does not appear to be related to the level of infection of the host since parasitaemias were similar in all strains tested. In addition, the level of non-specific polyclonal B cell activation as assessed by the enumeration of anti-TNP antibody-producing cells in the spleens of infected animals was found to be similar in CBA/N, CBA/CaT6 and A/J mice. In contrast, the level of circulating immune complex-like material was lower in CBA/N mice at a time when mice of other strains were dying from the effects of the infection. Finally, although CBA/N mice survive a T. brucei infection for a longer time interval, they exhibit a non-specific immunosuppression similar to that seen in conventional mice.

Delayed-type hypersensitivity in mice immunized with Trypanosoma rhodesiense antigens.

When mice were immunized intravenously, subcutaneously, or by the footpad route with formaldehyde-killed Trypanosoma rhodesiense, delayed-type hypersensitivity was elicited by the use of frozen-thawed trypanosomal antigen. The delayed footpad swelling technique was used to measure delayed hypersensitivity. Hypersensitivity induction was dose dependent (greater than or equal to 10(6) formaldehyde-treated T. rhodesiense) and was affected by the route of immunization. The footpad route induced higher levels of hypersensitivity than other routes of immunization. Mice immunized with a single dose of formaldehyde-treated antigen and challenged with live T. rhodesiense did not survive. Yet, mice immunized subcutaneously with formaldehyde-treated antigen and then injected with frozen-thawed antigen and challenged 28 days after immunization survived. The results suggest that T-cell activation, manifested by delayed hypersensitivity responses, was a necessary component in the protective response, perhaps functioning in a helper cell capacity.

Prevention of recrudescent malaria in nude mice by thymic grafting or by treatment with hyperimmune serum.

Nude mice died when infected with the normally avirulent malarial parasite Plasmodium berghei yoelii. Furthermore, malaria recrudesced in Nu/Nu mice after the termination of acute disease by treatment with clindamycin. Recrudescence was not observed in Nu/Nu mice that had been grafted with thymic tissue or treated with hyperimmune serum. Mice mad B cell deficient by treatment with anti-mu-chain serum also died when infected with P. berghei yoelii. The data suggest that a crucial role of the thymus in preventing recrudescent malaria in this model system is to provide a helper function in the production of protective antibody.

Delayed immune reactions in mice immunized with malarial antigen.

Mice were immunized subcutaneously, intravenously or in a footpad with antigens prepared from a lethal strain of Plasmodium berghei yoelii. A delayed footpad swelling (DFS) reaction was observed 4 days after immunization, and was detectable at least 42 days after immunization. However, IV immunization was the least efficacious is producing hypersensitivity. Regardless of the type of antigen used for immunization, mice responded similarly when live parasites were used to elicit DFS. This study revealed that hypersensitivity depended on route of immunization and type of antigen.

Cyclophosphamide pretreatment and protection against malaria.

Mice pretreated with cyclophosphamide were able to overcome infection from a lethal malarial strain. The development of resistance was preceded by increased hypersensitivity to malarial antigens. Hypersensitivity was demonstrable by a delayed footpad swelling technique.

Cross reactivity between Anaplasma marginale and two Plasmodium species as demonstrated by passive hemagglutination.

Two types of antigens were prepared from each of 3 partially purified preparations of Anaplasma marginale, Plasmodium lophurae, and P berghei. Hemagglutination tests were conducted with homologous serums to detect antigenic relationships between these organisms. Serums were also absorbed with both homologous and heterologous antigen preparations. Cross reactivity between these organisms was observed.