Identification of hairy cell leukemia subset defining p35 as the human homologue of Ii

Targeting the MHC Class II antigen presentation pathway in cancer immunotherapy

The success of immunotherapy relies on the participation of all arms of the immune system and the role of CD4+ T lymphocytes in preventing tumor growth is now well established. Understanding how tumors evade immune responses holds the key to the development of cancer immunotherapies. In this review, we discuss how MHC Class II expression varies in cancer cells and how this influences antitumor immune responses. We also discuss the means that are currently available for harnessing the MHC Class II antigen presentation pathway for the development of efficient vaccines to activate the immune system against cancer.

Genetic modulation of tumor antigen presentation

An effective cancer-cell vaccine is created by expressing major-histocompatibility-complex (MHC) class II molecules without the invariant chain protein (Ii) that normally blocks the antigenic-peptide-binding site of MHC class II molecules at their synthesis in the endoplasmic reticulum. Such tumor-cell constructs are created either by the transfer of genes for MHC class IIalpha and beta chains, or by the induction of MHC class II molecules and Ii protein with a transacting factor, followed by Ii suppression using antisense methods. Preclinical validation of this approach is reviewed with the goal of using this immunotherapy for metastatic human cancers.

Decreased expression of Ii-derived p25 and of P67/69 in hairy leukemic cells

Hairy leukemic cells had altered expressions of accessory proteins (Ii, Ip, p70, p25) which associated intracellularly with class II MHC molecules. Immunoprecipitates from [35S]methionine, pulse-chase labeled leukemic cells, B-lymphoblastoid cells, and Burkitt's lymphoma cells were examined after 2-dimensional, polyacrylamide gel electrophoresis. The class II MHC-associated Ii chain was present in all three cell types, but the Ii-derived p25 protein was not found in HCL cells. Ip, the sialic acid-derivatized form of Ii, was well expressed in BLCL and Raji cells, but weakly in HCL cells. P70 was strongly expressed in BLCL and Raji cells, but negligibly in HCL cells. These alterations might reflect deficient mechanisms for antigen processing and presentation by these leukemic cells.

B-cell lymphomas of high-grade malignancy frequently lack HLA-DR, -DP and -DQ antigens and associated invariant chain

The expression of HLA-DR, HLA-DP and HLA-DQ antigens was studied in an unselected series of 66 B-cell lymphomas by means of immunohistology using monoclonal antibodies against non-polymorphic determinants in a sensitive immunoperoxidase technique. In addition, the expression of the MHC class-II antigen-associated invariant chain (li) was examined. The tumors were classified according to the Kiel classification, 30 being of high-grade and 36 being of low-grade malignancy. Only 6 lymphomas of high-grade and 16 lymphomas of low-grade malignancy showed coordinate strong expression of all HLA class-II antigens and invariant chain as observed in the normal peripheral B cell. Six further tumors of high-grade and 8 tumors of low-grade malignancy contained tumor-cell subsets with reduced expression of one or several of the antigens. Eighteen lymphomas of high-grade and 12 lymphomas of low-grade malignancy contained varying tumor-cell subsets that were negative for HLA-DR, -DP, -DQ and li in a selective or combined manner. Three highly malignant tumors were devoid of all class-II antigens and li; 2 highly malignant tumors expressed invariant chain only. The presence of high-grade malignancy was significantly correlated with the occurrence of tumor cells lacking HLA-DR (p = 0.004), HLA-DP (p = 0.013), HLA-DQ (p = 0.007) or li (p = 0.024).

Hairy leukemic cells which hyperexpress Ii do not demonstrate Ii genome alterations by restriction endonuclease analysis

The finding of increased expression and apparently altered processing of Ii in hairy leukemic cells led us to test for Ii genomic alteration by Southern-type Ii cDNA hybridization to leukemic spleen DNA cleaved with a series of restriction endonucleases. Some insertions, deletions, or point mutations, potentially detectable by this technique, might correlate to alteration in expression and function of Ii (and indirectly, class II antigens). No changes in genomic structure of Ii were detected in DNA isolated from spleens of five patients with hairy cell leukemia, compared with DNA preparations from peripheral blood cells of nineteen healthy blood donors. These experiments were consistent with the view that gross structural alteration of the Ii genome had not occurred in hairy leukemic cells.

Hairy cell leukemia

Hairy cell leukemia is a chronic lymphoproliferative disorder that has been recognized as a separate clinical pathologic entity for the last 25 years. After a decade of discussions about the origin of the neoplastic cell, it has now been well established that hairy cells represent a certain, rather mature stage of B-cell differentiation. Evidence for this has been derived from studies using immunophenotyping with monoclonal and polyclonal antibodies, cytochemistry, and immunoglobulin gene rearrangement. For many years, splenectomy was the only therapy of proven value in hairy cell leukemia. For patients who showed insufficient response to the operation, chemotherapy with low-dose alkylating agents was moderately successful, whereas polychemotherapy often resulted in excessive toxicity. More recently, therapy with alpha-interferon has been shown to be very promising, whereas deoxycoformicin may be an attractive alternative. These new advances in immunology and therapy are reviewed.

RAB-1: a new monoclonal antibody to leukemic hairy cells

RAB-1, a new monoclonal antibody (McAb) to human leukemic hairy cell (HC) was produced. Using indirect immunofluorescence methods and microscopic or flow cytometric analysis, it was found that the RAB-1 antigen was expressed on few resting B cells and not on resting T lymphocytes, platelets, monocytes, erythroid and myeloid cells. RAB-1 expression on malignant cells was as follows: strongly positive in 15/15 hairy cell leukemia (HCL), negative with non-T and T-acute lymphoblastic leukemia and T-chronic lymphocytic leukemia (CLL); weakly expressed on myeloma and Waldenstrom cells; moderately on 10-25% of the cells in 4/10 B-CLL and 6/10 B lymphomas and in 7/7 B-prolymphocytic leukemia (PLL). Amongst human cell lines that were tested, RAB-1 reacted strongly with one HC line, moderately with the EBV-lymphoblastoid Daudi and Raji Burkitt's lines and was not expressed on Ramos, ALL, myeloid and erythroid cell lines. Normal B cells activated with PWM or anti-mu beads, and malignant B cells activated with anti-mu and TPA did not show an increase of expression of RAB-1 antigen. Interestingly, 30-40% of T4-Class II antigen positive cloned cells and T cells activated with PHA and Con.A expressed RAB-1, suggesting that this McAb recognizes surface molecule, newly induced during T-cell activation and constitutively expressed on HC and some B-cell malignancies.

Expression of p35 in hairy leukemic cells from Japanese patients

Spiro and coworkers found a 35000 dalton membrane protein (p35) expressed abundantly in hairy cells of a subset of white, American patients with hairy cell leukemia. They subsequently identified p35 to be the human homologue of murine Ii, an electrophoretically invariant protein associated with Ia molecules. Using related analytical techniques, we have studied leukemic cells of two blood and one splenic samples from three Japanese patients with hairy cell leukemia and have demonstrated abundance of p35 in the splenic and one of the blood samples. The second blood sample was negative for p35 by our method of analysis, but the same hairy cells became positive for p35 at 2 months in culture and negative again at 4 months in culture. All 3 samples of this patient (fresh hairy cells and cultured cells at 2 and 4 months) remained consistently positive for Ia and for light chain-restricted immunoglobulin. Control cells from one each of acute lymphoblastic leukemia and Burkitt's lymphoma were negative for abundant p35 expression after culture as well as in the fresh state. One can conclude that the Japanese form of hairy cell leukemia, while varying in several distinct clinical and laboratory features from hairy cell leukemia in caucasians, is characterized also by abundant expression of p35 as seen in a subset of white patients. In addition, this expression of p35 is developed by hairy leukemic cells in culture initially but is lost upon longer term culture, in parallel with the level of tartrate-resistant acid phosphatase reactivity.

Differential effect of TPA and n-butyrate on induction of Ii and EBV antigens in the P3HR-1 lymphoblastoid cell line

The aim of this study was to test whether EBV induction by TPA or n-butyrate was related directly to hyperexpression of Ii, an electrophoretically invariant, 35 000 dalton, HLA-DR antigen-associated glycoprotein which is abundantly detected in EBV freshly transformed cells and is enhanced by EBV superinfection of lymphoblastoid cell lines. P3HR-1 lymphoblasts were treated with n-butyrate or TPA in variable doses and durations. The augmented expression of Ii, EBV antigens (EA and VCA), DNA synthesis, and cell growth and viability were monitored. n-Butyrate induced hyperexpression of Ii at 2 days with a maximal effective dose of 4 mM, induced EBV antigens (EA and VCA) in 36 per cent of the cells at 2 days, inhibited DNA synthesis and cell growth, and was not cytolytic at 48 h when Ii induction was maximal. TPA did not induce hyperexpression of Ii, induced EBV antigens (EA) in 30 per cent of the cells at 4 days, did not inhibit DNA synthesis and cell growth, and was not cytolytic in the time course and doses studied. Ii expression, therefore, did not appear to be an obligatory consequence of EBV antigen induction. Ii induction might be related to an effect of EBV inducers on cellular DNA synthesis, or on control of the cell cycle, or directly upon Ii gene regulation.

Enhanced Ii expression after n-butyrate treatment of a P3HR-1 Burkitt's lymphoma subline which does not express HLA-D

Treatment of P3HR-1 Burkitt's lymphoma cultured cells with 4 mM n-butyrate for 48 h induced the abundant expression of a 35 000 dalton, microsomal membrane protein which was demonstrated to be the electrophoretically invariant Ii molecule. To prove this point, [35S]methionine-labelled, microsomal membrane proteins or immunoprecipitates of such detergent-solubilized proteins were subjected to electrophoresis either in SDS gels or in two-dimensional, nonequilibrium pH gradient gels. The induced p35 molecule was judged to be Ii by molecular weight and isoelectric characteristics and by immune complex associations. The abundant expression of Ii on butyrate-treated P3HR-1 cells mimicked the high level of expression of p35 or Ii on leukemic cells of a subset of patients with hairy cell leukemia. Alpha and beta chains of the HLA-D complex were absent from the P3HR-1 cell line and present in the Jijoye parent from which mutant P3HR-1 was derived. This relatively simple model can lead to the study of inducible synthesis, processing and expression of Ii, with or without HLA-D alpha and beta chains.