Limited T-cell repertoire in renal allograft and allogeneic melanoma transmitted by the graft.

In a patient with metastatic melanoma transmitted by the renal allograft, HLA serves as an alloantigen per se and is associated with tumor antigens at the same time. The influence of this antigeneic pattern on the Vbeta T-cell repertoire in an allogeneic melanoma, allograft, and peripheral blood mononuclear cells (PBMC) was assessed by polymerase chain reaction. Vbeta13.1 and 19 were found in both the melanoma and the graft. Vbeta14 was detected only in the melanoma and Vbeta6 was detected only in the kidney. PBMC revealed an unrestricted Vbeta pattern. Markers for cytotoxic activity of T cells--granzyme B and perforin--were not expressed during immunosuppressive therapy as clinically reflected in a nonrejecting allograft and in a progressing melanoma. In vitro PBMC proliferated to recombinant interleukin-2, whereas recombinant interferon-gamma did not augment this response. Initiation of immune therapy, in addition to discontinuation of immunosuppression, might support the rejection of the allogeneic tumor by dominant Vbeta T cells.

[Immunologic, alloantigen-dependent factors in chronic graft rejection]. / Immunologische, alloantigenabhängige Faktoren in der chronischen Transplantatabstossung.

BACKGROUND: The pathogenesis of chronic renal allograft rejection is still speculative. Amongst other factors immune-mediated graft injury is proposed. Since the allo-antigen is specifically recognized by the variable (V) alpha and beta chains of the T-cell receptor, a restricted T-cell repertoire might support the notion of allo-antigen involvement in chronic rejection. METHODS: By the means of semiquantitative polymerase chain reaction the V beta families 1-20 were assessed in allograft biopsies with histologically confirmed chronic and acute rejection. At the same time the V beta repertoire was analyzed in PBMC. RESULT: The intragraft V beta repertoire was limited to 1 to 3 dominant V beta families in chronic and acute rejection. The response was highly individual and did not correlate to the type or degree of HLA mismatches. The T-cell repertoire in PBMC was polyclonal and did not reflect the immune response in the graft. CONCLUSION: The finding of a restricted V beta repertoire in both forms of rejection might indicate an immunological basis not only for acute, but also for ongoing chronic rejection. Tailor-made antibodies against the dominant V beta clones might provide a tool for selective immunosuppression in both entities of rejection targeting only those T cells which were activated by allo-antigens.

Restricted T cell V beta repertoire in renal allografts during acute and chronic rejection.

Allo-MHC specific antigen recognition might not only be involved in acute, but also in chronic rejection. The clonotypic specificity of the T-cell receptor to recognize all-MHC is located in the variable (V) alpha and beta chain. A restricted T-cell receptor repertoire could support an immunological basis for chronic rejection. The novel feature of this study is that V beta repertoire was assessed in ongoing chronic rejection before end-stage renal failure and in acute rejection. V beta s 1 to 20 were quantitated by PCR in PBMC and biopsies of rejecting renal allografts. The V beta pattern in PBMC demonstrated a polyclonal distribution. However, the intragraft V beta repertoire was restricted to 1 to 3 dominant V betas and highly individual in 9 of 12 patients. Number and type of the HLA mismatch and the time interval between transplantation and biopsy did not correlate to the V beta distribution. The individual response is attributed to genetic predisposition factors of the recipient. Therefore, the restriction of the V beta repertoire indicates allo-MHC dependent immune processes not only in acute, but also in ongoing chronic rejection. Tailor-made antibodies against dominant V betas might offer specific individual immunosuppression in treating both acute and ongoing chronic rejection.

High rates of Ac/Ds germinal transposition in Arabidopsis suitable for gene isolation by insertional mutagenesis.

Overexpression of the Activator (Ac) transposase gene in Arabidopsis thaliana resulted in a minimal germinal transposition frequency of 27% in which independent Dissociation (Ds) transposition events were observed. Molecular analysis of 45 F1 generation Ac/Ds plants indicated that high rates of somatic excision had occurred, and independent germinal insertions were identified in F2 generation progeny plants. A tandem cauliflower mosaic virus (CaMV) promoter fused to two different Ac coding sequences significantly increased the rate of Ds transposition. The CaMV-Ac fusions activated single and multiple copies of two different Ds elements, DsDHFR and Ds35S-1, and reciprocal crosses resulted in similar transposition frequencies. The improved rate of independent germinal transposition observed makes Arabidopsis an ideal system for insertional mutagenesis.

Characterisation of a new allele of pale cress and its role in greening in Arabidopsis thaliana.

A recessive mutant with white leaves was identified in a screen of a population of T-DNA-tagged Arabidopsis thaliana plants. The mutation is lethal, but plants develop almost to maturity under sterile conditions. The white areas in leaves are devoid of developed chloroplasts, but the plants frequently develop green sectors which contain green chloroplasts. Molecular characterisation of the affected gene revealed that the mutant is allelic to pale cress (pac), a recently described mutation, and was therefore named pac-2. Sequencing of cDNAs and the genomic region revealed several noteworthy features of this genetic locus. In pac-2 the T-DNA had inserted in the region of the promoter and abolished transcription of the PAC gene completely. Cytokinin induced greening in mature, white homozygous pac-2 plants, and therefore is likely to be responsible for the greening observed in callus and shoots induced on roots from such plants. However, the PAC transcript was found to be absent in both white leaves and green callus. Thus, since cytokinin induced greening in the absence of PAC RNA this plant hormone appears to be able to bypass PAC function.