T cell receptor gamma (TCRG) gene rearrangements in T cell acute lymphoblastic leukemia reflect 'end-stage' recombinations:: implications for minimal residual disease monitoring

The T cell receptor gamma (TCRG) gene configuration was established in a large series of 126 T cell acute lymphoblastic leukemia (T-ALL) patients using combined Southern blotting (SB) and heteroduplex PCR analyses. The vast majority of T-ALL (96%) displayed clonal TCRG gene rearrangements, with biallelic recombination in 91% of patients. A small immature subgroup of CD3(-) T-ALL (n = 5) had both TCRG genes in germline configuration, three of them having also germline TCRD genes. In five patients (4%) combined SB and PCR results indicated oligoclonality. In five rearrangements detected by SB, the V gamma gene segment could not be identified suggesting illegitimate recombination. Altogether, 83% of TCRG gene rearrangements involved either the most upstream V gamma 2 gene (including four cases with interstitial deletion of 170 bp in V gamma 2) andlor the most downstream J gamma 2.3 segment, which can be perceived as 'end-stage' recombinations. Comparative analysis of the TCRG gene configuration in the major immunophenotypic subgroups indicated that TCR gamma delta(+) T-ALL display a less mature immunogenotype as compared to TCR alpha beta(+) and most CD3(-) cases. This was reflected by a significantly increased usage of the more downstream V gamma genes and the upstream J gamma 1 segments. Comparison between adult and pediatric T-ALL patients did not show any obvious differences in TCRG gene configuration. The high frequency, easy detectability, rare oligoclonality, and frequent 'end-stage' recombinations make TCRG gene rearrangements principal targets for PCR-based detection of minimal residual disease (MRD) in T-ALL. We propose a simple heteroduplex PCR strategy, applying five primer combinations, which results in the detection of approximately 95% of all clonal TCRG gene rearrangements in T-ALL. This approach enables identification of at least one TCRG target for MRD monitoring in 95% of patients, and even two targets in 84% of T-ALL.