REARRANGED IMMUNOGLOBULIN LIGHT-CHAIN GENES AS MINIMAL RESIDUAL DISEASE MARKERS IN INTERMEDIATE-GRADE AND HIGH-GRADE MALIGNANT B-CELL NON-HODGKINS-LYMPHOMA

Minimal residual disease (MRD) defection in B cell non-Hodgkin's lymph oma (NHL) patients has been shown to be possible using the rearranged heavy (IgH) chain gene as a tumor marker. To explore a second independ ent tumor marker, we used specific PCR primer sets to identify tumor-s pecific rearranged Ig light chain (IgL) genes. Rearranged IgL genes we re amplified from lymphoma DNA by multiplex PCR using separate primer sets for the Ig kappa and the Ig lambda genes. They were considered to be of tumor origin if they were monoclonal, and if the same rearrange ment was isolated from at least two independent PCR products. From 12 out of 13 intermediate- and high-grade malignant NHL, PCR products cou ld be obtained with IgL specific primers. PCR products from five NHL w ere studied in detail by cloning and sequencing. The rearranged IgL ge nes showed 85-100% homology with their closest germ line counterparts. Intraclonal IgL sequence heterogeneity was studied in five lymphomas and detected in only one. Minimal disease was studied in three patient s by PCR, followed by Southern hybridization of the PCR product with a lymphoma-specific oligonucleotide probe, which allowed for detection of lymphoma DNA following 1000-fold dilution. Blood samples from one p atient, who is in long-term clinical remission, were negative for the lymphoma-specific rearranged Ig kappa gene. In the second patient the rearranged Ig lambda gene was detected during the first: clinical remi ssion, that was followed by a nodal relapse, but not during the second remission, that has been stable for almost 3 years now. The third pat ient was negative for the rearranged Ig lambda gene in blood samples u p to 102 months after diagnosis. Circulating lymphoma cells were defec ted in blood and bone marrow samples which were negative by morphologi cal and immunological criteria. Our studies show that the rearranged I gL gene can be used as a second independent tumor marker in intermedia te- and high-grade malignant NHL.