Review article Minimal residual disease detection in B-cell malignanciesby assessing IgH rearrangement K. Maloum 1 , O. Pritsch 2 and G. Dighiero 2 1 Hôpital Pitié-Salpêtrière, Département d'Hématologie, 47-83, Bd de l'Hôpital F-75651 Paris cedex 13, France 2 Institut Pasteur, Unité d'Immuno-Hématologie et d'ImmunoPathologie, F-75724 Paris cedex 15, France Received May 16, 1997 / Accepted May 28, 1997 Key words: MRD B-cell malignancies IgH genes PCR Correspondence to: K. Maloum Abstract In B-cell malignancies, the uniqueness of the immunoglobulin heavy chain locus (IgH) clonal rearrangement provides a useful marker for the detection of minimal residual disease (MRD) after treatment. During the last decade, several techniques have been proposed and used for detecting MRD. In this review, we report the current PCR based techniques dealing with amplification of the VDJ segment since the CDR3 region is unique to each IgH rearrangement. The sensitivity of these techniques varies considerably with a detection level of one tumoral cell in 10 -2 to 10 -6 normal cells. Accurate and sensitive assessment of MRD may have profound impact in the clinical management of patients with hematologic malignancies. Although, a majority of studies have shown a good correlation between the rapidity or extent of the reduction in the number of tumoral cells and the subsequent relapse, other studies demonstrated substained positivity of PCR in patients in long term remission. Thus, current clinical studies of MRD should establish whether MRD predicts relapse uniformly and, therefore, justifies intensification of therapy in positive cases, or whether it simply detects leukemic cell populations whose proliferative potential has been altered by chemotherapy. Immunoglobulin (Ig) variable domains are the product of combinatorial joining of V(D)J gene segments [27, 43]. Multisequence comparisons of variable domains have shown that each variable domain contains three regions of extensive sequence variability, termed the complementary determining regions (CDRs), and four regions of relative sequence stability, termed framework regions (FRs) [24]. The three light (L) chain CDRs and the three heavy (H) chain CDRs are juxtaposed to form the antigen-binding site of the antibody (Ab), as classically defined. In turn the FRs create a scaffold that surrounds, supports, and influences the conformation and structure of the CDRs [25]. CDRs 1 and 2, and FRs 1, 2 and 3 are entirely encoded by the V gene segments; and FR4 is encoded by the J genes. CDR3, the most variable portion of the nascent Ab, is created by V(D)J joining and lies at the center of the antigen binding site. Ig diversity can be enhanced through the process of somatic hypermutation which typically takes place in lymphoid germinal centers following exposure of the B-cell to antigen [51]. An additional and important source of diversity derives from the fact that junctional regions in Ig heavy chain (IgH) genes vary enormously in each clone of B lymphocytes due to the rearrangement of different VH, DH and JH gene segments as well as either the random deletion of germline nucleotides or the insertion of nontemplate-derived nucleotides ("N regions"), a reaction mediated by terminal deoxynucleotidyl transferase (TdT) [43, 44, 46]. Thus, the uniqueness of the Ig receptor constitutes a very reliable marker of the malignant clone as well as a suitable marker for minimal residual disease (MRD) detection. In acute lymphoblastic leukemia (ALL), several groups assessed MRD in the bone marrow of patients with pre-B ALL by using molecular techniques to detect the uniqueness VDJ rearrangement [15, 26, 34, 49, 50]. In