Generation of TSTA diversity. Looking for testable hypotheses

Characterization of a chemically homogeneous tumor antigen from a methylcholanthrene-induced sarcoma, Meth A

A tumor antigen isolated from the cytosol of a methylcholanthrene-induced sarcoma (Meth A) has been purified to homogeneity by the criteria of two-dimensional gel analysis and NH2- and COOH-terminal sequencing. The purified antigen has a mol. wt of 82,000 by SDS gel electrophoresis. However, the apparent mol. mass of the antigen was found to be 71,600 and 67,700 by gel filtration chromatography and sedimentation analysis, respectively. It is not a glycoprotein, possesses an acidic isoelectric point (6.0) and exists as dimeric and monomeric species. The dimer is not held together by disulfide bonds. The purified protein retains its ability to induce transplantation immunity in syngeneic hosts when challenged with Meth A sarcomas. Chemical analyses of the NH2- and COOH-termini gave the following sequences: NH2-PKPINVRVTTMDAELEFAIQPN and IDE(F,A)EM-COOH, respectively.

Autologous cellular immune response to primary and metastatic human melanomas and its regulation by DR antigens expressed on tumor cells

Evidence for heterogeneity of several biological features of human malignant melanoma (Me) like morphology, cytogenetics, oncogenes activation, antigenic expression, metastatizing capacity and procoagulant activity are briefly reviewed in an attempt to distinguish findings related to primary vs. metastatic lesions. In our own studies monoclonal antibodies were used to study expression of MHC class I, class II products and of Me-associated antigens (MAA) on primary and metastatic Me cells. High expression of class I antigens was found in a high percentage of both primary and metastatic tumors, whereas DR and MAA showed a significant variation (from 3 to 90% of cells) in expression both in primary and in metastatic Me. When autologous cell-mediated immune responses were evaluated, it was found that Me cells from primary tumors but not those from lymph node metastases were able to stimulate autologous lymphocytes to proliferate and become cytotoxic for autologous Me. Clonal analysis of cytotoxic lymphocytes was then carried out in order to see whether the lack of lymphocytes reactivity to metastatic cells was due to the absence or to a low frequency of cytotoxic cells in the unstimulated PBL. CTL clones cytotoxic for autologous Me (Auto-Me) cells were indeed isolated. Three classes of CTL clones were identified: 1) one which is cytotoxic for Auto-Me; 2) a second one which lyse Auto-Me and allogeneic Me; and 3) a third one which is cytotoxic for Auto-Me and allogeneic normal and neoplastic cells. Metastatic Me cells, however, had the ability to suppress the stimulation of autologous PBL by alloantigens or IL-2. This effect was dose-dependent and was not due to absorption of IL-2 by Me cells. Since it has been reported that Me cells express class II MHC antigens, we investigated whether there was any correlation between autologous immune responses and DR expression on Me cells. Autologous lymphocytes stimulation was found to occur only with DR+ Me cells from primary lesions, whereas metastatic cells, either DR+ or DR-, did not stimulate autologous PBL. Moreover, the suppressive effect of metastatic Me cells was associated with their expression of DR antigens. The modulation of DR antigens on Me cells by Interferon-gamma correlated positively with their suppressive capacity. Thus, it appears that primary Me can behave differently from the metastatic one in their interactions with the immune system of autologous host. These findings suggest that DR antigens on Me cells may have an important role in the regulation of autologous immune responses.

The effect of purification on the immunogenicity of tumor-specific transplantation antigens

Immunization with the tumor-specific transplantation antigens (TSTA) of experimental, chemically induced sarcomas engenders specific host resistance to challenge with viable, homotypic neoplastic cells. The strength of tumor resistance depends upon the physical state of the TSTA used for immunization. Treatment with 10(5)-10(6) irradiated tumor cells, a 2-log dose range, induces complete rejection of neoplastic challenges, while immunization within a 1-log dose range with crude 3 M KCl or with 2.5% butanol extracts containing TSTA evokes a weak state of resistance characterized by decreased outgrowth of tumor challenges, but not neoplastic regression. The reduced immunogenicity may be due to either contamination with substances that antagonize host resistance, for example by induction of suppressor cells, or an intrinsic limitation by virtue of the molecular properties of extracted compared with cell-surface TSTA. MCA-F and MCA-D, two noncross-reactive fibrosarcomas induced in C3H/HeJ mice with 3-methylcholanthrene, were employed to compare the relative immunogenic activity of intact tumor cells, 2.5% butanol extracts, and materials sequentially purified by preparative isoelectric focusing (pIEF), preparative isotachophoresis (pITP), and high performance gel permeation chromatography (HPGPC). Immunoprotective TSTA activity purified 50,000-fold by this protocol extended the effective dose range by four to five logs: 15 pg to 1.5 micrograms MCA-F or 1 pg to 10 ng MCA-D antigen-induced specific host resistance. However, despite the appreciable purification of TSTA, immunization with extracted materials only delayed neoplastic outgrowth. They induced neither immediate rejection nor only temporary progression of transplanted tumor cells. Thus, purified TSTA preparations by themselves lack the immunogenic properties of intact cells that result in maximal induction of tumor resistance.

Specificity of tumour associated transplantation antigens (TATA) of different clones from the same tumour

The TATA of two clones from the same murine methylcholanthrene-induced fibrosarcoma have been investigated by immunizing syngeneic mice with irradiated cells of one or both clones and challenging them 14 days later with viable cells. The tumour had been induced in a female backcross CBA mouse heterozygous for the A and B alloenzymes of phosphoglycerate kinase-1 (PGK-1). One clone expressed A and the other B, and both A and B hosts were used in the experiments. Each clone was found to possess strong TATA but there was no demonstrable cross reactivity. The clonal composition of tumours produced by inoculating mice with a mixture of the two clones was profoundly altered by prior immunization with one of them. A second experiment was performed with 3 clones from another tumour; these expressed PGK-1 A, B and AB respectively. Again, there was no evidence of immunological cross reactivity between the A and B clones, but there was some cross reactivity between the A clone and AB clone. These results, coupled with previous observations of changes in the clonal composition of pleoclonal murine fibrosarcomas in culture and on transplantation, suggest that the antigenic specificity of these tumours is less stable than is commonly supposed.