Evaluation of an oral CXCR3 antagonist in a rat model of acute cardiac allograft rejection

Noninvasive detection of renal allograft inflammation by measurements of mRNA for IP-10 and CXCR3 in urine

BACKGROUND

We explored the hypothesis that measurements of mRNA encoding interferon-inducible protein-10 (IP-10) or the chemokine receptor CXCR3 in urinary cells offer a noninvasive means of elucidating cellular traffic causing acute rejection of human renal allografts.

METHODS

We obtained 63 urine specimens from 58 renal allograft recipients who underwent 63 allograft biopsies to resolve the basis for graft dysfunction, and 27 additional urine samples from 24 other patients with stable allograft function. Twenty-seven of the 63 biopsies were classified as acute rejection, 20 as other, and 16 as chronic allograft nephropathy. We measured the levels of transcripts for IP-10 and CXCR3, and a constitutively expressed gene 18S rRNA in the urine specimens and correlated transcript levels with renal allograft diagnosis.

RESULTS

mRNA levels of IP-10 (P < 0.0001) or CXCR3 (P < 0.0001) but not the levels of 18S rRNA (P= 0.56) predicted intragraft cellular traffic causing acute rejection. Receiver-operating characteristic curve analysis demonstrated that acute rejection can be predicted with a sensitivity of 100% and a specificity of 78% using the (log-transformed) cutoff value of 9.11 copies of IP-10, and with a sensitivity of 63% and a specificity of 83% using the cutoff value of 11.59 copies of CXCR3. Immunohistologic analysis of allograft biopsies showed exuberant expression of IP-10 and CXCR3 during acute rejection whereas both were absent in grafts with stable function.

CONCLUSION

Our investigation demonstrates that intragraft cellular events associated with acute rejection of human renal allografts can be noninvasively identified by measurements of mRNA for IP-10 and CXCR3 in urinary cells.

Chemokine receptor-dependent alloresponses

Immunologists have typically viewed alloreactivity schematically as a function of antigen presentation, expansion of alloreactive T and B cells within regional lymphoid tissues, and cellular infiltration and destruction of an allograft. Actual details of the steps between immune activation and accumulation of effector cells within a graft typically have not received much attention. However, just how cells "know" to move to and migrate within a graft or not is proving to be of increasing interest, as the chemokine-dependent mechanisms underlying leukocyte recruitment to a transplant are dissected. Experimentally, chemokine receptor targeting can prolong or induce permanent allograft survival, despite preservation of alloresponses within secondary lymphoid tissues, whereas current immunosuppressive protocols have only modest effects on chemokine production and leukocyte homing. Recent knowledge of the chemokine-dependent nature of allograft rejection, acceptance, and tolerance induction are presented as a basis for understanding the rationale for preclinical trials of chemokine receptor-targeted therapies currently underway in primate recipients of solid organ allografts.