New intra-renal graft genes associated with tolerance or rejection

Recipient type mononuclear cells infiltrating kidney allografts have different phenotypes and functions according to the fate of the graft. We hypothesized that different genetic programs were involved in rejected or accepted tissues and thus, transcripts that correlated with the clinical status could be identified by a differential expression strategy. This strategy was applied to miniature swine class II matched, class I disparate kidney grafts, which are accepted in recipient animals treated for 12 days with Cyclosporin A (CsA).

The mRNA differential display RT-PCR technique (DDRT-PCR) was used to detect clinical status-specific transcripts. cDNA templates for this analysis were derived from biopsies of accepted (CsA treated) and rejected (untreated) kidney grafts 8 days post-transplantation.

A first screening procedure identified 23 PCR products differentially amplified in either tolerant or rejector samples. Nucleotide sequence of these partial transcripts showed that 11 out of 23 (48%) sequences had unknown open reading frames while 12 had substantial homology to known sequences. To validate the approach, rejection-associated (RA) cDNA 1 (RA-1) was characterized further. The results indicated that RA-1 is the porcine equivalent of secreted protein acidic and rich in cysteine (SPARC). Expression studies demonstrated that upregulation of SPARC gene transcription preceded other indicators of kidney dysfunction and correlated with the extent of graft infiltration.

DDRT-PCR appears to be a powerful technique to identify genes differentially expressed in grafted tissues that correlate with tolerance or rejection. One of the gene transcripts identified through this method, SPARC, may be a reliable marker of tissue injury consequent to cellular infiltration and rejection.