Large Granular Lymphocyte Leukemia: Clonality Reconsidered.

Background: T-cell large granular lymphocyte (LGL) leukemia is widely considered to represent a monoclonal proliferation of lymphocytes. Clonality assessment methods have evolved from Southern blots (first-generation) to polymerase chain reaction with heteroduplex electrophoresis (second-generation) to high-resolution capillary electrophoresis (third-generation) testing.

Aims: To determine if third-generation T-cell clonality assays result in a higher frequency of oligoclonal results, to compare the concordance for testing at the T-cell receptor (TCR) gamma (TCRG) and TCR beta (TCRB) loci, and to compare the clinical characteristics of patients with monoclonal vs. oligoclonal TCRs.

Methods: The study population consisted of patients from August 1999-April 2007 with elevated circulating LGLs and cytopenia(s). TCRG locus clonality was determined by both the heteroduplex method and capillary electrophoresis in 35 patients. 89 samples were tested for TCRG and TCRB clonality using the Biomed II PCR primer sets and capillary electrophoresis on an ABI 3100 automated DNA sequencer. Determinations of clonality were made independently by three pathologists blinded to the clinical characteristics of the patients.

Results: A total of 93 patients (median age 50 years, 53% female) were evaluated. Median absolute neutrophil count was 1.56 × 10⁹/L (range 0.2–7.8 × 10⁹/L), median lymphocyte count was 1.81 × 10⁹/L (range 0.6–13 × 10⁹/L), and median hemoglobin was 13 g/dL (range 6.3–17.4 g/dL). The concordance rate for TCRG clonality testing by the heteroduplex and capillary electrophoresis methods was only 40%. The primary difference was a striking increase in the frequency of oligoclonal results by the capillary electrophoresis method (p= 0.00007). All of these samples appeared monoclonal by the lower resolution heteroduplex assay (Table 1). Concordance for clonality for TCRG vs. TCRB was 54% (Table 2). All samples had monoclonality or oligoclonality demonstrated at TCRG or TCRB, but only 26% were monoclonal at both loci. The clinical characteristics for the 23 patients with monoclonal TCRG and TCRB appeared similar to the 23 patients with oligoclonal TCRG and TCRB. The median age in both groups was 53 years, with 61% of patients in each group requiring treatment after a median of 36.8 and 38.6 months of follow-up, respectively.

Discussion: The high resolution of capillary electrophoresis appears to result in a much greater proportion of oligoclonal TCRG results, which by the older heteroduplex method would have been considered monoclonal. Furthermore, the concordance rate at TCRG and TCRB appears to be remarkably low. Though oligoclonal T-cell populations are generally believed to be transient and reactive processes, the clinical characteristics of our oligoclonal and monoclonal cohorts did not differ significantly.

Conclusion: Capillary electrophoresis frequently identifies patients with oligoclonal TCR whose clinical features are indistinguishable from those of patients with classic monoclonal LGL leukemia.