Class switch DNA recombination (CSR) is the mechanism that diversifies the biological effector functions of antibodies. Activation-induced cytidine deaminase (AID), a key CSR player, targets IgH switch (S) regions, which contain 5′-AGCT-3′ repeats in their core. How AID is recruited to S regions remains unclear. Here we show that 14-3-3 adaptor proteins play an important role in CSR. 14-3-3 proteins specifically bind 5′-AGCT-3′ repeats, are upregulated in B cells undergoing CSR and are recruited together with AID to the S regions involved in CSR events (Sμ→Sγ1, Sμ→Sγ3 or Sμ→Sα). Moreover, blocking 14-3-3 by difopein, deficiency in 14-3-3γ or expression of a dominant negative 14-3-3σ mutant impaired recruitment of AID to S regions and decreased CSR. Finally, 14-3-3 proteins interact directly with AID and enhance AID-mediated in vitro DNA deamination, further emphasizing the important role of these adaptors in CSR.

Immunoglobulin (Ig) gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) are critical for the maturation of the antibody response. These processes endow antibodies with increased antigen-binding affinity and acquisition of new biological effector functions, thereby underlying the generation of memory B cells and plasma cells. They are dependent on the generation of specific DNA lesions and the intervention of activation-induced cytidine deaminase as well as newly identified translesion DNA polymerases, which are expressed in germinal center B cells. DNA lesions include mismatches, abasic sites, nicks, single-strand breaks, and doublestrand breaks (DSBs). DSBs in the switch (S) region DNA are critical for CSR, but they also occur in V(D)J regions and possibly contribute to the events that lead to SHM. The nature of the DSBs in the Ig locus, their generation, and the repair processes that they trigger and that are responsible for their regulation remain poorly understood. Aberrant regulation of these events can result in chromosomal breaks and translocations, which are significant steps in B-cell neoplastic transformation.Keywords activation-induced cytosine deaminase (AID); class switch recombination (CSR); DNA lesion; double-strand break (DSB); error-prone DNA repair; lesion bypass or translesion DNA polymerase; pol ι; pol θ; pol ζ; somatic hypermutation (SHM); V(D)J recombination

Patients with chronic lymphocytic leukemia (CLL) may develop diffuse large B-cell lymphoma (DLBL), also known as Richter's syndrome. Mutational status of immunoglobulin (Ig) heavychain variable region (V H ) genes have prognostic impact in CLL. Patients with mutated V H genes have a stable disease, whereas patients with unmutated V H gene have more aggressive disease. The mutational status of CLLs that transform to DLBL is unknown. To reveal whether Richter's syndrome occurs in CLLs with mutated or unmutated V H genes, we have performed mutational analysis on serial specimens from eight patients. CLL and DLBL tumorclones were identical in five cases and they were different in three cases. Six CLLs expressed unmutated and two cases expressed mutated V H genes. In five of the six unmutated CLLs, the DLBL clones evolved from CLL tumorclones and the V H genes expressed by DLBLs were also unmutated. In one unmutated and two mutated CLLs, the DLBLs expressed mutated V H genes, but in these three cases the DLBL tumorclones developed as independent secondary neoplasm. These results suggest that Richter's syndrome may develop in both mutated or unmutated CLLs, but clonal transformation of CLL to DLBL occur only in the unmutated subgroup of CLL.

The aim of the present study was to classify colorectal carcinoma (CRC) into molecular subtypes, based on immunohistochemical (IHC) assessments. A total of 112 CRC samples were molecularly classified based on the expression levels of epithelial-mesenchymal transition (EMT)-associated IHC markers. A total of three molecular subtypes were defined: Epithelial, membrane positivity for E-cadherin and β-catenin, negative for vimentin; mesenchymal, E-cadherin-negative, nuclear β-catenin-and vimentin-positive; and hybrid cases, epithelial tumor core and mesenchymal tumor buds. Most of the cases were diagnosed as moderately differentiated adenocarcinoma (n=89; 79.46%). The majority of cases (n=100; 89.28%) exhibited a mismatch repair proficient status (microsatellite stable CRCs). A predominance of epithelial-type (n=51; 45.54%) and hybrid CRCs (n=47; 41.96%) was observed, whereas a few cases (n=14; 12.50%) were classified as mesenchymal-type CRCs. This molecular classification was associated with pathological stage (P<0.01), pT stage (P=0.04), pN stage (P<0.01), the grade of tumor budding (P=0.04), and maspin expression in both the tumor core (P=0.04) and the invasion front (P<0.01). The mesenchymal-type cases predominantly exhibited lymph node metastases, high-grade budding and a tendency towards maspin nuclear predominance. All epithelial-type cases with maspin-only expression (n=18) were non-metastatic. Patients with CRC of the epithelial subtype and those with a lymph node ratio (LNR) ≤0.15 presented the best overall survival, followed by those with hybrid and mesenchymal subtypes. Nuclear maspin positivity was more frequent in cases with a high-budding degree compared with those with a low-budding degree (P=0.03). The EMT-associated molecular classification of CRCs may be used to identify the most aggressive CRCs, which show a mesenchymal phenotype, high-budding degree, maspin nuclear positivity and lymph node metastases. The pN stage, LNR and budding degree of patients, which can be evaluated with maspin expression, remain the most important prognostic factors.

Mediastinal (thymic) large B-cell lymphoma (MBL) has been defined as a subtype of diffuse large B-cell lymphoma (DLBL) arising in the mediastinum with characteristic clinicopathological features. It has been postulated that MBL arise from non-circulating thymic B-cells and represent a distinct lymphoma entity, however, the histogenesis of the disease is not yet fully understood. In order to clarify the histogenetic derivation of MBL and to determine the relationship of MBL to thymic B-cells we have analyzed the nucleic acid sequences of immunoglobulin (Ig) heavy chain variable region (VH) and 5' noncoding region of BCL-6 genes in normal thymic B-cells and six cases of MBL. Thymic B-cells and tumor cells of MBLs displayed hypermutated VH and/or BCL-6 genes but intraclonal divergence did not associate with these mutations. Since somatic mutations of the IgVH and BCL-6 genes are histogenetic markers of B-cell transit through the germinal centre (GC), these results suggest that both thymic B-cells and MBLs derived from GC or an equivalent environment where B-cells underwent somatic hypermutation. The similar pattern of mutations of IgVH and BCL-6 genes found in thymic B-cells and MBLs further supports the theory that MBLs originate from thymic B-cells.

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Despite the description of several new prognostic markers, colorectal cancer still represents the third most frequent cause of cancer-related death. As immunotherapy is considered a therapeutic alternative in such patients, neutrophil-to-lymphocyte (NLR) and lymphocyte-to-monocyte ratio (LMR) are hypothesized to provide reliable prognostic information. A retrospective study was conducted on 1052 patients operated on during 2013–2019 in two clinical hospitals from Hungary and Romania. Inclusion criteria targeted patients over 18 years old, diagnosed with rectal cancer, with preoperatively defined NLR and LMR. The overall survival rate, along with clinical and histopathological data, was evaluated. Overall survival was significantly associated with increased NLR (p = 0.03) and decreased LMR (p = 0.04), with cut-off values of 3.11 and 3.39, respectively. The two parameters were inversely correlated (p < 0.0001). There was no statistically significant association between tumor stage and NLR or LMR (p = 0.30, p = 0.06, respectively). The total mesorectal excision was especially obtained in cases with low NLR (p = 0.0005) and high LMR (p = 0.0009) values. A significant association was also seen between preoperative chemoradiotherapy and high NLR (p = 0.0001) and low LMR (p = 0.0001). In patients with rectal cancer, the preoperative values of NLR and LMR can be used as independent prognostic parameters. An NLR value of ≥3.11 can be used to indicate the response to preoperative chemoradiotherapy, but a low chance of sphincter preservation or obtaining a complete TME. Higher values of NLR and lower values of LMR require a more attentive preoperative evaluation of the mesorectum.