DNA vaccines to target the cancer testis antigen PASD1 in human multiple myeloma.

We previously described PASD1 as a new cancer testis antigen in multiple myeloma (MM) that is retained post-therapy, suggesting the use of vaccination strategies to induce anti-PASD1 immunity in a setting of minimal residual disease. We have focused on DNA fusion gene vaccines, coupling fragment C domain (DOM) of tetanus toxin with PASD1 sequence, and examined efficacy in Human Leukocyte Antigen (HLA)-A2 (HHD) transgenic mice using a human MM cell line expressing PASD1 protein and chimeric HLA-A2 class I molecules as target. DNA vaccines encoded two HLA-A2-restricted epitopes (p.DOM-PASD1(1), p.DOM-PASD1(2)) and full-length PASD1 (p.DOM-PASD1FL). p.DOM-PASD1(1) proved superior to p.DOM-PASD1(2) in generating T-cell responses in HHD mice, able to lyse the chimeric murine RMA-HHD cells. Boosting by electroporation significantly enhanced p.DOM-PASD1(1). Only p.DOM-PASD1(1) induced cytotoxic T-lymphocytes (CTLs) were able to lyse human MM target cells expressing endogenous antigen. The p.DOM-PASD1FL vaccine predominantly induced strong PASD1(1) over PASD1(2) T-cell immune responses, indicative of immunodominance. Importantly, p.DOM-PASD1FL generated immune-mediating killing of native chimeric MM cells, in the absence of exogenous added peptide, implicating PASD1(1) specific CTLs. These data demonstrate that PASD1-derived epitopes are both efficiently and selectively processed and presented by native human MM cells. Notably, they permit the use of PASD1-encoding DNA vaccine therapy in a clinical setting.

Defining origins of malignant B cells: a new circulating normal human IgM(+)D(+) B-cell subset lacking CD27 expression and displaying somatically mutated IGHV genes as a relevant memory population.

In probing the cell of origin in malignant B cells, an imprint of somatic hypermutation (SHM) in immunoglobulin (Ig) variable (V) region genes delineates antigen encounter, and identifying the precise pathway generating SHM in the normal B-cell counterpart becomes relevant. SHM remains the definitive memory imprint in normal human B cells, but CD27 expression also delineates memory. Recently, dye extrusion adenosine triphosphate-binding transporter assays identified circulating isotype-switched memory B cells that lacked CD27, yet exhibited low levels of SHM. To extend findings, we report a pre-switched CD27(-ve) circulating memory B-cell population in normal blood using comparable assays, and isolated CD19(+)IgM(+)D(+)CD27(-ve) cells (>99% purity) for the analysis of IGHV5/IGHV3-IGHM transcripts. Of these (n=334), approximately 78% were germ line and naive B cell derived. Strikingly, 21.9% of the transcripts were mutated. They showed 3-5 mutations (13.5% of sequences) and >5 mutations (8.4% of sequences) per transcript. Accrual of mutations in a subset of CD19(+)IgM(+)D(+)CD27(-ve) cells define a new circulating pre-switched memory B-cell pool, present in substantial numbers in the population harboring naive B cells. These CD19(+)IgM(+)D(+)CD27(-ve) memory B cells may have a distinct lineage and function, and seem relevant to understanding origins of malignant B cells, in particular those of hairy cell leukemia cells, which display mutated V genes yet lack CD27 expression.

Frequent expression of HAGE in presentation chronic myeloid leukaemias.

Cancer testis (CT) antigens provide attractive targets for cancer-specific immunotherapy. Although CT genes are expressed in some normal tissues, such as the testis and in some cases placenta, these immunologically protected sites lack MHC I expression and as such, do not present 'self' antigens to T cells. To date, CT genes have been shown to be expressed in a range of solid tumours, but rarely in haematological malignancies. We have extended previous studies to investigate the expression of a comprehensive range of CT genes (MAGE-A1, -A3, -A6, -A12, BAGE, GAGE, HAGE,LAGE-1, NY-ESO-1 and RAGE) for their expression in a cohort of acute and chronic myeloid leukaemia patient samples. CT expression was not detected in 20 normal bone marrow or peripheral blood stem cell samples. In acute myeloid leukaemia (AML) nine of the 26 (35%) samples analysed expressed one or more of the CT genes with six of the samples (23%) expressing HAGE. In chronic myeloid leukaemia (CML) 24 of 42 (57%) presentation chronic myeloid leukaemia (CML) patient samples expressed one or more CT antigen with 23 expressing HAGE. We have shown that HAGE is frequently expressed in CML, and to a lesser extent in AML patient samples. This is the first demonstration of HAGE gene expression in myeloid leukaemia patients and the frequent expression of HAGE at disease presentation opens up the possibility of early immunotherapeutic treatments.

The occurrence and significance of V gene mutations in B cell-derived human malignancy.

The classification of B cell tumors has relevance for refining and improving clinical strategies. However, consensus has been difficult to establish, and although a scheme is now available, objective criteria are desirable. Genetic technology will underpin and extend current knowledge, and it is certain to reveal further subdivisions of current tumor categories. The Ig variable region genes of B cell tumors present a considerable asset for this area of investigation. The unique sequences carried in neoplastic B cells are easily isolated and sequenced. In addition to acting as clone-specific markers of each tumor, they indicate where the cell has come from and track its history following transformation. There is emerging clinical value in knowing whether the cell of origin has encountered antigen and has moved from the naive compartment to the germinal center, where somatic mutation is activated. This is amply illustrated by the subdivision of chronic lymphocytic leukemia into two subsets, unmutated or mutated, each with very different prognosis. Other tumors may be subdivided in a similar way. Microarray technology is developing rapidly to probe gene expression and to further divide tumor categories. All these genetic analyses will provide objective data to enhance both our understanding of B cell tumors and our ability to treat them.

Tumor cells of hairy cell leukemia express multiple clonally related immunoglobulin isotypes via RNA splicing.

Hairy cell leukemia (HCL) derives from a mature B cell and expresses markers associated with activation. Analysis of immunoglobulin variable region genes has revealed somatic mutation in most cases, consistent with an origin from a cell that has encountered the germinal center. One unusual feature of hairy cells (HCs) is the frequent expression of multiple immunoglobulin heavy chain isotypes, with dominance of immunoglobulin (Ig)--G3, but only a single light chain type. The origin and clonal relationship of these isotype variants have been unclear. In order to probe the isotype switching status of HCL, RNA transcripts of V(H)DJ(H)--constant region sequences from 5 cases of typical HCL, all expressing multiple surface immunoglobulin isotypes, were analyzed. Tumor V(H)DJ(H)--C(mu) sequences were identified and found to be somatically mutated (range, 1.4% to 6.5%), with a low level of intraclonal heterogeneity. Additional immunoglobulin isotypes of identical V(H)DJ(H) sequence were also identified, including IgD (5 of 5), IgG3 (5 of 5), IgG1 (3 of 5), IgG2 (2 of 5), IgA1 (4 of 5), and IgA2 (1 of 5). Derivation of multiple isotypes from individual cells was demonstrated by analyzing transcripts in single sorted cells from one patient, with evidence for coexistence of isotype variants in 10 of 10 cells. These findings indicate that clonally related multiple isotypes coexist in single HCs, with individual isotypes presumably generated via RNA splicing. Production of IgG3 appears common, but IgG1, IgG2, IgA1, and IgA2 also arise, indicating a continuing influence of a directed process on the tumor clone. These HCs appear to be arrested at the point of isotype switch, where RNA processing may precede deletional recombination. (Blood. 2001;98:1174-1181)

IgG-secreting lymphoplasmacytoid leukaemia: a B-cell disorder with extensively mutated VH genes undergoing Ig isotype-switching frequently associated with trisomy 12.

We investigated 16 patients with elevated serum monoclonal IgG and a leukaemic B-cell lymphocytic disorder different from multiple myeloma. Their clinical history was that of a non-aggressive disease with dominant splenomegaly and long survival. Whereas abnormal blood and bone marrow cells were predominantly small lymphocytes with a few lymphoplasmacytoid cells, histopathological features included a lymphoplasmacytic infiltrate in eight cases. Most frequently, abnormal blood cells displayed a CD19+CD5-CD23+/- immunophenotype different from that of chronic lymphocytic leukaemia, except in two cases with a CD19+CD5+CD23+ phenotype. Interestingly, a coexistent serum monoclonal IgM and/or surface IgMG+ with identical light chain was identified in 10 patients, whereas in the remaining six patients only IgG expression was determined. VH gene analysis was performed in eight patients to investigate the clonal origins of tumour cells. All cases utilized the VH3 family, with evidence of extensive somatic mutations and intraclonal homogeneity in all cases. VH gene analysis indicated a clonal relationship between cells expressing IgM and IgG, with one case being biclonal. Cytogenetic evaluation showed a high incidence of trisomy 12 (60%) and 13q14 deletion (40%). In conclusion, we have described an unusual subset of low-grade lymphoma with high-serum IgG and frequent lymphoplasmacytoid features in which tumour cells derive from post-follicular memory B cells undergoing isotype switching with some cases arrested at both the IgM and IgG stage and others as IgG-positive cells only.

Somatic mutation of bcl-6 genes can occur in the absence of V(H) mutations in chronic lymphocytic leukemia.

Somatic mutation in immunoglobulin variable (V) region genes occurs largely in the germinal center and, after neoplastic transformation, imprints V genes of B-cell tumors with the mutational history of the cell of origin. Recently, it has been found that chronic lymphocytic leukemia (CLL) consists of 2 subsets, each with a different clinical course, one with unmutated V(H) genes consistent with a naive B cell, and the other with mutated V(H) genes consistent with transit through the germinal center. However, somatic mutation also occurs at another distinct locus, the 5' noncoding region of the bcl-6 gene, in both B-cell tumors and in normal germinal center B cells. To probe the suggestive link between the occurrence of mutations in V(H) and bcl-6 genes, we analyzed the nature of somatic mutation at these distinct loci in the 2 CLL subsets. Unexpectedly, we found no such link in the CLLs defined by unmutated V(H) genes, with 4 of 10 cases clearly showing mutations in bcl-6. In those CLLs defined by somatically mutated V(H) genes, 4 of 9 cases predictively showed bcl-6 mutations. The frequency of bcl-6 mutations was comparable in both subsets, with mutations being biallelic, and in 3 of 8 cases indicative of clonal origins. Surprisingly, intraclonal variation, which is not a feature of V(H) genes in CLL, was found in 6 of 8 cases in both subsets. These data indicate that somatic mutation of the V(H) and bcl-6 loci may not necessarily occur in tandem in CLL, suggesting diverse pathways operating on the 2 genes.

V(H) gene analysis of IgM-secreting myeloma indicates an origin from a memory cell undergoing isotype switch events.

IgM-secreting plasma cell tumors are rare variants of typical isotype-switched multiple myeloma with a similar disease outcome. To probe the origin and clonal history of these tumors, we have analyzed V(H) gene sequences in 6 cases. Potentially functional tumor-derived V(H) genes were all derived from V(H)3, with the V(3-7) gene segment being used by 4 of 6. All were somatically mutated, with a mean deviation from germline sequence of 5.2% (range, 3.1% to 7.1%). The distribution of replacement mutations was consistent with antigen selection in 4 of 6 cases, and no intraclonal heterogeneity was observed. Clonally related switched isotype transcripts were sought in 4 cases, and Cgamma transcripts with tumor-derived CDR3 sequence were identified in 2 of 4. These findings indicate that IgM-secreting myelomas are arrested at a postfollicular stage at which somatic mutation has been silenced. Isotype switch variants show the cell of origin to be at the IgM to IgG switch point. These features indicate that the final neoplastic event has occurred at a stage immediately before that of typical isotype-switched myeloma. One possibility is that IgM myeloma involves the previously identified precursor cell of typical myeloma.

B cell maturation in relation to multiple myeloma.

Maturation of a normal B-cell precursor to a mature plasma cell involves rearrangement and somatic mutation of the immunoglobulin variable (V) region genes. These events occur at distinct stages of development, and when a B cell undergoes neoplastic transformation, the genetic imprint reflects the clonal history of the cell of origin. Sequence analysis of V-genes can reveal bias as compared with the available repertoire, possibly reflecting a role for superantigen in stimulation of certain B cells. It can also indicate if the tumour cell has encountered the site of somatic mutation in the germinal centre, and if this mechanism is still active post-transformation. Analysis may also reveal a potential influence of persistent antigen in driving tumour growth. Genetic evidence supports the concept that tumour cells are not frozen at a single point of differentiation, but are able to move through certain limited stages. For myeloma, V-gene analysis indicates that the malignant cell population is likely to be derived from an antigen-selected plasma cell, but that a less mature minor B cell population of identical sequence may coexist. In contrast, benign plasma cell tumours can include B cells still undergoing somatic mutation. In both malignant and benign disease, transcripts of clonally-related alternative isotypes have been identified V-gene analysis is contributing to the diagnosis, monitoring and understanding of B-cell tumours, and may facilitate the development of rational approaches to therapy.

DNA vaccines with single-chain Fv fused to fragment C of tetanus toxin induce protective immunity against lymphoma and myeloma.

Vaccination with idiotypic protein protects against B-cell lymphoma, mainly through anti-idiotypic antibody. For use in patients, DNA vaccines containing single-chain Fv derived from tumor provide a convenient alternative vaccine delivery system. However, single-chain Fv sequence alone induces low anti-idiotypic response and poor protection against lymphoma. Fusion of the gene encoding fragment C of tetanus toxin to single-chain Fv substantially promotes the anti-idiotypic response and induces strong protection against B-cell lymphoma. The same fusion design also induces protective immunity against a surface Ig-negative myeloma. These findings indicate that fusion to a pathogen sequence allows a tumor antigen to engage diverse immune mechanisms that suppress growth. This fusion design has the added advantage of overcoming potential tolerance to tumor that may exist in patients.

VH gene analysis of clonally related IgM and IgG from human lymphoplasmacytoid B-cell tumors with chronic lymphocytic leukemia features and high serum monoclonal IgG.

An unusual group of human B-cell tumors with cellular features of chronic lymphocytic leukemia or lymphoplasmacytoid leukemia, together with high levels of a monoclonal IgG serum protein, has been investigated. Analysis of tumor-derived VH genes of neoplastic B lymphocytes was used to determine the clonal relationship between the IgM expressed or secreted by the tumor cells and the IgG serum paraprotein. In all five cases, VH gene sequences showed transcripts of IgM and IgG of common clonal origin. Sequences were derived from VH3 (4 of 5) and VH1 (1 of 5) families and were all highly somatically mutated with strong evidence for antigen selection. There was no intraclonal variation detectable in either IgM or IgG sequences. In 3 of 5 cases, in which monoclonal IgM and IgG were found in serum, the VH genes combined to Cmu or Cgamma showed identical mutational patterns. However, in 2 of 5 cases, in which IgM was confined to cell expression with only monoclonal IgG in serum, sequences of the VH transcripts of IgM and IgG showed many shared mutations but also numerous differences. In these cases, the level of mutation was similar in IgM and IgG and both appeared to be antigen selected. In summary, the final neoplastic event in this group of tumors has apparently occurred at the point of isotype switch from IgM to IgG, leading to dual isotype synthesis. In the group that secreted both isotypes, the mutation pattern was identical, indicating either synthesis by a single cell, or silencing of mutational activity before switching. In the group that did not secrete IgM, cells of each isotype were distinct and reflected a divergent mutational history.

Myeloma VL and VH gene sequences reveal a complementary imprint of antigen selection in tumor cells.

In multiple myeloma, sequence studies of VH genes used to encode clonal Ig in neoplastic plasma cells have shown a common pattern of extensive somatic hypermutation. A further consistent feature of these VH sequences is a complete lack of intraclonal variation. These findings indicate that the malignant cell arises at a mature, postfollicular stage of B-cell development. However, only a minority of cases have a distribution of somatic mutations in VH consistent with a prior role for antigen in selecting the B cell of origin. To complement these studies, and to take further the investigation of a role for antigen in the clonal history of myeloma, we have investigated tumor-derived VL sequences from bone marrows of 15 patients. All sequences (9V kappa and 6V lambda A) were potentially functional and 5 of 15 had evidence for N-region additions. All had undergone extensive somatic hypermutation, and showed no intraclonal variation. In 4 of 15 cases, the distribution of mutations revealed a significant (P < .05) clustering of replacement mutations in the CDR sequences, indicating a role for VL in selection by antigen. Comparison with the VH sequences used by the same tumor cells showed that, if significant clustering was present, it was in either VH or VL but not both. Altogether, 10 of 15 V-regions showed evidence for antigen selection, suggesting that the B cell of origin has behaved as a normal germinal center B cell. Deductions concerning a role for antigen selection may require both VH and VL sequences for validation.

Ig VH gene mutational patterns indicate different tumor cell status in human myeloma and monoclonal gammopathy of undetermined significance.

Plasma cell tumors display a wide spectrum of clinical progression, ranging from aggressive multiple myeloma to a benign form known as monoclonal gammopathy of undetermined significance (MGUS), which requires no treatment. Because both diseases involve mature Ig-secreting plasma cells, the reason for this variation in malignant behavior is unclear. However, assessment of malignant potential is desirable for choice of treatment protocols. Ig variable (VH) gene sequences analysis has previously shown the tumor cell of multiple myeloma to be postfollicular, with mutated homogeneous clonal sequences indicating no continuing exposure to the somatic hypermutation mechanism, and this was confirmed in 7 of 7 patients. Comparison of the VH gene sequences in the monoclonal cells in MGUS yielded a different result, with 3 of 7 patients demonstrating mutated heterogeneous sequences consistent with the tumor cells remaining under the influence of the mutator. In 1 of 3 of these patients, an IgM-positive precursor cell was identified that expressed heterogeneous VH sequences similar to those of the isotype-switched plasma cell. These results indicate that the clonal cells in MGUS differ from those in myeloma and suggest that the difference may reflect malignant potential.