Induction and maintenance of cytotoxic T lymphocyte (CTL) activity specific for a primary endogenous tumor was investigated in vivo. The simian virus 40 T antigen (Tag) expressed under the control of the rat insulin promoter (RIP) induced pancreatic β-cell tumors producing insulin, causing progressive hypoglycemia. As an endogenous tumor antigen, the lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) was introduced also under the control of the RIP. No significant spontaneous CTL activation against GP was observed. However, LCMV infection induced an antitumor CTL response which efficiently reduced the tumor mass, resulting in temporarily normalized blood glucose levels and prolonged survival of double transgenic RIP(GP × Tag2) mice (137 ± 18 d) as opposed to control RIP-Tag2 mice (88 ± 8 d). Surprisingly, the tumor-specific CTL response was not sustained despite the facts that the tumor cells continued to express MHC class I and LCMV-GP–specific CTLs were present and not tolerized. Subsequent adoptive transfer of virus activated spleen cells into RIP(GP × Tag2) mice further prolonged survival (168 ± 11 d), demonstrating continued expression of the LCMV-GP tumor antigen and MHC class I. The data show that the tumor did not spontaneously induce or maintain an activated CTL response, revealing a profound lack of immunogenicity in vivo. Therefore, repetitive immunizations are necessary for prolonged antitumor immunotherapy. In addition, the data suggest that the risk for induction of chronic autoimmune diseases is limited, which may encourage immunotherapy against antigens selectively but not exclusively expressed by the tumor.

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RESUMO.-As variações nos parâmetros hematológicos são utilizadas com intuito de avaliar o grau de treinamento ou estado clínico do animal. A avaliação hematológica de eqüinos em repouso tem sido objeto de estudo, a fim de estabelecer uma relação com treinamento ou capacidade atlética. Objetivou-se avaliar o perfil hematológico de eqüinos submetidos à prova de Team Penning, correlacionando o sexo e freqüência da atividade física. Mediante punção da veia jugular externa coletaram-se dois mL de sangue de 29 eqüinos, 18 machos e 11 fêmeas, em repouso (Momento I) e após o exercício (Momento II Variations in hematologic parameters are used to assess the degree of training or clinical state of the animal. The hematologic evaluation of horses at rest has been an object of study in order to establish a correlation with training or athletic capacity. The purpose of this study was to evaluate the hematologic profile of horses subjected to Team Penning competitions, correlating sex and frequency of physical activity. Two milliliters of blood were drawn through a puncture made in the external jugular vein from 29 horses, 18 males and 11 females, at rest (Moment I) and after exercising (Moment II). The blood samples were processed in an ABC VET automated veterinary hematology analyzer (Horiba ABX Diagnostics). The animals were divided into Group A, B, C and D according to the number of times they participated in the competition. The values of globular volume, hemoglobin, erythrocytes, rod-shaped segmented neutrophils and monocytes increased after the physical exercise, unlike the number of lymphocytes and eosinophils, which decreased. A comparison of the before/after exercise correlations showed no significant differences (p<0.05) between males and females. In addition, it was found that the value of the MI/MII ratio for the globular volume, hemoglobin and number of erythrocytes varied according to the frequency of the exercise. It was concluded that the Team Penning competition produces hematologic alterations in horses, which are affected by the frequency of exercising, regardless of sex.INDEX TERMS: Equus caballus, exercise, hematology.