Cancer vaccines genetically engineered to produce interleukin 2 have been investigated intensively in a series of animal models and are at the point of entering into clinical trials. In this study we demonstrate a strong correlation between the rate of interleukin 2 production and the protection efficiency of murine S91 melanoma cell (clone M-3) vaccines. Best immunization is achieved with vaccines producing medium interleukin 2 levels of 1000-3000 units per
Adenovirus entry into its host cell transiently permeabilizes the cell allowing the coentry of reagents such as DNA. We compare here adenovirus inactivation with beta-propiolactone and several psoralen derivatives, seeking reagents that disrupt the viral genome without impairing the viral entry functions. No virus replication can be detected after 8-methoxypsoralen (8-MOP) modification. Viral transcription is not detectable by Northern analysis, and reverse transcriptase/PCR analysis demonstrates at least a 1000-fold decrease in viral transcription after 8-MOP treatment. Using [3H]8-MOP, the psoralen is found to enter the virus capsid and react throughout the viral genome, with approximately one psoralen modification per 100 bp of viral DNA. This inactivated adenovirus allows us to deliver DNA to target cells without interference from adenovirus gene expression or replication. Furthermore, we can now study the host cell response to adenovirus entry without the complications of adenovirus gene expression.
Although both CD4+ and CD8+ T cells are clearly required to generate long-lasting anti-tumor immunity induced by s.c. vaccination with interleukin 2 (IL-2)-transfected, irradiated M-3 clone murine melanoma cells, some controversy continues about the site and mode of T-cell activation in this system. Macrophages, granulocytes, and natural killer cells infiltrate the vaccination site early after injection into either syngeneic euthymic DBA/2 mice or athymic nude mice and eliminate the inoculum within 48 hr. We could not find T cells at the vaccination site, which argues against the concept that T-cell priming by the IL-2-secreting cancer cells occurs directly at that location. However, reverse transcription-PCR revealed transcripts indicative of T-cell activation and expansion in the draining lymph nodes of mice immunized with the IL-2-secreting vaccine but not in mice vaccinated with untransfected, irradiated M-3 cells. We therefore propose that the antigen-presenting cells, which invade the vaccination site, process tumor-derived antigens and, subsequently, initiate priming of tumor-specific T lymphocytes in lymphoid organs. These findings suggest a three-stage process for the generation of effector T cells after vaccination with IL-2-secreting tumor cells: (i) tumor-antigen uptake and processing at the site of injection by antigen-presenting cells,(ii) migration of antigen-presenting cells into the regional draining lymph nodes, where T-cell priming occurs, and (iii) circulation of activated T cells that either perform or initiate effector mechanisms leading to tumor cell destruction.
A full-length cDNA plasmid of foot-and-mouth disease virus has been constructed. RNA synthesized in vitro by means of a bacteriophage SP6 promoter inserted in front of the cDNA led to the production of infectious particles upon transfection of BHK-21 ceUs. These particles were also found to be highly infectious for primary bovine kidney cells as well as for baby mice. The difficulty in cloning the foot-and-mouth disease virus cytidyl tract in Escherichia coli was circumvented by joining two separate cloned parts, representing the S and L fragments of the genome, and, in a second step, inserting a dC-dG homopolymer. Homopolymeric sequences of up to 25 cytidyl residues did not lead to the production of virus. Replicons containing poly(C) tracts long enough to permit virus replication were first established in yeast cells. One of these constructs could also be maintained in E. coli and was used to produce infectious RNA in vitro. The length of the poly(C) sequence in this cDNA plasmid was 32 nucleotides. However, the poly(C) tracts of two recombinant viruses found in transfected BHK-21 cells were 60 and 80 nucleotides long, respectively. Possible mechanisms leading to the enlargement of the poly(C) tract during virus replication are discussed.
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