Highly Focused Clonal Composition of CD8+ CD28neg T Cellsin Aqueous Humor of Fuchs Heterochromic Cyclitis

Abstract Fuchs heterochromic cyclitis (FHC) is characterized by a predominant CD8 + T cell subset infiltrating the anterior chamber, but the clonal composition of these T cells is unknown. In the present study, T cell repertoire diversity of the accumulating T cells was analyzed to investigate if a high degree of restriction could indicate antigen-driven immune response. Aqueous humor (AH) and peripheral blood cells were collected in two patients with FHC. T cell repertoire diversity was screened by T cell receptor (TCR) BV family expression. In one patient, several BV gene segments were used by lymphocytes from the AH but with over-representation of BV16 that accounted for around half of the expressed intraocular repertoire. In the other patient, a more restricted TCRBV usage was found in AH, as only BV15 and BV18 were expressed in the ocular sample. In this patient, virtually all AH CD8 − T-cells were CD28- and CD57-negative by three-color flow cytometry, an immunophenotype suggestive of past antigenic stimulation. High resolution immunoscope analysis of TCRBV CDR3 profiles and sequencing of subcloned TCRBV-BJ PCR products evidenced a highly restricted TCRBV-BJ usage, since virtually all the intraocular cells comprise only five clonotypes in this patient. Unique peaks of CDR3 length were found in BV15 joined to BJ2S1, BJ2S3 and especially BJ2S5, in AH but did not predominate in blood. Conversely, identical clonotypes using rearranged BV18 and BJ2S7 gene segments were detected in both AH and peripheral blood. Maintenance of the TCRBV18-BJ2S7 clonotypes in aqueous humor was demonstrated over 6 months in this patient, with a switch in the predominance of two clonotypes. Our results show the presence of a finite number of CD8 + CD28 neg T cell clonotypes, which suggests an antigen-driven process and the involvement of these T cells in the pathogenesis of FHC.