Molecular basis of a unique tumor antigen of radiation leukemia virus-induced leukemia B6RV2: its relation to MuLV gp70 of xenotropic class

Hybridomas secreting monoclonal antibodies that reacted with the B6 radiation leukemia virus (RadLV)-induced leukemia B6RV2 were produced by fusion of BALB/c NS-1 myeloma cells with spleen cells from (BALB/c X B6)F1 mice immunized with B6RV2. By direct and absorption analyses with 28 B6 and BALB/c leukemias, the monoclonal antibodies NU7-4 and NU7-99 were shown to react only with B6RV2, indicating that they recognized an individually distinct antigen on B6RV2 that was identified previously with conventional (BALB/c X B6)F1 anti-B6RV2 serum. Another monoclonal antibody, NU1-132, showed relatively restricted reactivity with B6 RadLV leukemias. These three monoclonal antibodies all precipitated material of approximately 80,000 daltons, which is the same size as that precipitated by anti-xenotropic MuLV gp70 serum. Sequential immunoprecipitation analysis revealed that the molecules precipitated by NU7-4 were not removed by pretreatment of NU7-99 or NU1-132 and that the molecules precipitated by NU7-99 were not removed by NU7-4 or NU1-132. The molecules precipitated by NU1-132 were partially removed by pretreatment with NU7-4, but not with NU7-99. The molecules precipitated by these three monoclonal antibodies were removed by pretreatment with anti-xenotropic gp70. These results suggested heterogeneity of the xenotropic MuLV gp70-related molecules expressed on B6RV2 and a possible relation between serologically defined unique tumor antigens and gp70-related molecules.     

The immunotherapeutic effects in tumor-bearing mice of Ly-6 monoclonal antibodies

In vivo administration of Ly-6 mAb which recognize lymphoid differentiation Ag encoded for by the Ly-6 gene complex were found to have significant beneficial immunotherapeutic effects in tumor-bearing mice. The effectiveness of the mAb treatment in mice bearing sarcomas, leukemias, or melanomas was dependent on the host and not the tumor Ly-6 phenotype. The treatment was effective in nu/nu mice, although a more pronounced inhibition of tumor growth occurred in immunocompetent mice. The effectiveness of the therapy in immunocompetent mice was dependent on the dose of mAb and was influenced by the immunogenicity of the tumor. It ranged from significant growth inhibition of weakly immunogenic tumors to complete rejection of strongly immunogenic tumors. The results of cell-mediated cytotoxic assays of splenocytes from mAb-treated mice indicated that Ly-6 mAb treatment induced and/or augmented tumor-specific CTL as well as NK cell activity in these mice. Ly-6 mAb treatment represents a novel method for tumor immunotherapy using mAb recognizing lymphoid differentiation Ag with functional activities.     

Frequent involvement of the fim-3 region in Friend murine leukemia virus-induced mouse myeloblastic leukemias.

fim-3 is a new proviral integration region involved in 23% (16 of 68) of Friend murine leukemia virus-induced myeloblastic leukemias. This region is distinct from 20 oncogenes and from putative oncogenes tested so far. Proviruses are integrated in a 16-kilobase region, always in the same orientation. No RNA expression of fim-3 was detected.     

Prevalence of antigen receptor variants in human T cell lines and tumors

Previously, we have shown that a human T acute lymphoblastic leukemia cell line, HPB-ALL, exhibits clonal heterogeneity within its Ag receptor, as revealed by varying reactivity patterns with a panel of anti-idiotype mAb. We now extend these findings to another human T acute lymphoblastic leukemia cell line, SUP-T13, and to two fresh human chronic lymphocytic leukemias, JE and EF. In the two cell lines, two types of Ag receptor variants could be found: those that retained a receptor molecule but lost reactivity with an anti-idiotype mAb (idiotype variants), and those which had lost surface receptor expression completely (receptor-negative variants). The idiotype variants, at least in HPB-ALL, have differentially glycosylated receptor alpha-chains from the parent. The receptor-negative cells, in HPB-ALL as well as in SUP-T13, produce cytoplasmic receptor and CD3 proteins but do not transport them to the surface. Neither idiotype nor receptor-negative variants could be detected in either of the fresh tumors of chronic lymphocytic leukemias. The limit of sensitivity in these analyses was about 0.05%. We conclude that antigen receptor variants can spontaneously occur in cell lines derived from acute lymphoblastic leukemias, but are infrequent in chronic lymphocytic leukemias in vivo, and that therapy with anti-idiotype mAb may be a viable strategy for these malignancies.     

The role of HLA class I antigens in recognition of melanoma cells by tumor-specific cytotoxic T lymphocytes. Evidence for shared tumor antigens

CTL lines were established in vitro by stimulating patient lymphocytes with autologous melanoma cells in the presence of IL-2. Resulting CTL lines lysed autologous melanoma and failed to lyse several allogeneic melanomas or K562. The mechanism of target cell recognition by autologous tumor-specific CTL was evaluated in this system, using several CTL lines: DT6, DT105, DT141, DT166, DT169, and DT179. Autologous melanoma lysis was inhibited by W6/32, mAb directed against HLA class I Ag, but not by L243, mAb directed against HLA class II Ag. CTL from DT6, DT141, DT166, DT169, and DT179 lysed fresh and cultured allogeneic melanomas, which shared the HLA-A2 Ag, but failed to lyse allogeneic melanomas, which shared B-region or C-region Ag, or shared no HLA class I Ag. CTL from DM141 lysed DM93, which shared A2 and Bw6, but failed to lyse DM105, which shared only Bw6. DM105 CTL failed to lyse allogeneic melanomas that shared HLA-A1, or that shared B or C region Ag, but they did lyse allogeneic melanoma DM49, which expressed an A region Ag that either was A10 or was serologically cross-reactive with A10. A T cell leukemia line, three EBV transformed B cell lines, and a pancreatic cancer line, all of which expressed HLA-A2, were not lysed by DM6 or DM179 CTL. Furthermore, HLA-matched nonmelanomas failed to inhibit autologous tumor lysis in cold target inhibition assays, whereas an HLA-A2+ allogeneic melanoma, DM93, inhibited autologous tumor lysis as effectively as the autologous tumor itself. HLA-A2, and possibly other HLA-A-region Ag, appear to function in HLA-restricted recognition of shared melanoma associated Ag by CTL.     

Marked difference in the in vivo antitumor efficacy between two immunotoxins targeted to different epitopes of common acute lymphoblastic leukemia antigen (CD10). Mechanisms involved in the differential activities of immunotoxins.

In the present study, two isotype-matching mAb, SN5d and SN5, which are directed toward two distinctively different epitopes of common acute lymphoblastic leukemia Ag (CD10) but show a very similar binding affinity to leukemia cells, were compared for their in vivo antitumor activity after conjugated to ricin A chain (RA). Our recently established nude mouse model carrying an ascitic tumor of NALM-6 human pre-B leukemia cells was used as the tumor model. A marked difference was observed in the in vivo antitumor efficacy between SN5d-RA and SN5-RA; SN5d-RA was much more effective than SN5-RA. Several experiments were carried out to gain information concerning the mechanisms involved in the different antitumor efficacy of the two immunotoxins. Although naked (unconjugated) mAb SN5d was much less effective than SN5d-RA conjugates in the in vivo tumor suppression, mAb SN5d was more effective than mAb SN5 in the in vivo tumor suppression. Additionally, marked differences were found between SN5d and SN5 in the induction of antigenic modulation and in the regulation of Ag biosynthesis and expression. Binding of SN5 to NALM-6 leukemia cells caused strong antigenic modulation (down-regulation of Ag expression) and strongly down-regulated Ag biosynthesis and cell surface expression of new Ag. In contrast, binding of SN5d to NALM-6 leukemia cells caused little modulation of overall cell surface expression of common acute lymphoblastic leukemia Ag; the decrease of old Ag by endocytosis after binding to mAb SN5d was compensated by newly exocytosed cell-surface expressed Ag. The present results appear to reveal a novel mechanism which regulates cytotoxic activities of antibodies and immunoconjugates.     

Subpopulations of B cells in germinal centers. III. HJ6, a monoclonal antibody, binds globoside and a subpopulation of germinal center B cells.

To identify surface Ag uniquely expressed on human germinal center B cells, we produced a mouse mAb, HJ6. When tonsillar lymphocytes were examined, HJ6 did not label T cells and labeled only about half of PNA+ B cells that were HK23-. HJ6 did not label mononuclear cells from peripheral blood, splenocytes, and any of 29 cell lines including 23 B cell lines. This binding pattern of HJ6 was very similar to that of a mAb named 5B5. It was shown previously that 5B5 bound a glycolipid named CTH (CD77) and its Ag was expressed on HK23- PNA+ tonsillar lymphocytes and Burkitt's lymphoma cell lines. Despite the similarity, HJ6 differed from 5B5: HJ6 did not stain Burkitt's lymphoma cell lines and stained PNA+ tonsillar lymphocytes in the presence of a large concentration of galactose. When its binding to isolated glycolipids was studied, HJ6 was found to bind globoside and Forssman Ag and not to other glycolipids including CTH. When its binding to neutral glycolipids extracted from tonsillar lymphocytes was studied, HJ6 bound only globoside; Forssman Ag was not detected in tonsillar lymphocytes. Taken together, we conclude that globoside is a B cell Ag expressed on a subpopulation of germinal center B cells.     

The HB-6, CDw75, and CD76 differentiation antigens are unique cell- surface carbohydrate determinants generated by the beta-galactoside alpha 2,6-sialyltransferase

Expression of the beta-galactoside alpha 2,6-sialyltransferase (alpha 2,6-ST) was shown to regulate the generation of multiple cell-surface differentiation antigens (Ags) that may be necessary for lymphocyte function. A new mAb was produced, termed HB-6, that was shown to identify a novel neuraminidase-sensitive cell-surface Ag expressed by subpopulations of human lymphocytes and erythrocytes. In attempting to isolate a cDNA encoding the HB-6 antigen by expression cloning, a cDNA encoding the alpha 2,6-ST (EC 2.4.99.1) was obtained. Since expression of the alpha 2,6-ST protein was shown to be limited to the Golgi apparatus, the cell-surface HB-6 Ag was demonstrated to be the product of alpha 2,6-ST activity. Interestingly, alpha 2,6-ST expression also generated two other neuraminidase-sensitive lymphocyte cell-surface differentiation Ags, CDw75, and CD76. The HB-6, CDw75, and CD76 mAb identified distinct Ags that were differentially expressed by different B cell lines and exhibited different patterns of expression in tissue sections. These results indicate that alpha 2,6-ST expression is a critical regulatory step in the formation of the Ags that are recognized by these mAb, and that an alpha 2,6-linked sialic acid residue is an essential component of each Ag. Thus, expression of a single ST can result in the generation of multiple distinct antigenic determinants on the cell surface which can be distinguished by mAb and may have regulatory roles in lymphocyte function.     

Incidence and phenotypic heterogeneity of Moloney virus-induced leukemias: a multigenic control

The incidence of leukemias was established in mice of different inbred strains inoculated with Moloney leukemia virus (M-MuLV), and a complex genetic control was found. To characterize the different steps of the host-virus relationship further, the degree of viremia, the appearance of leukemia, organ involvement, and the surface phenotype of leukemic cells were studied in individual mice. The results demonstrate that: a) The viremia was controlled by H-2 and non-H-2 genes. Three H-2 genes located in the I and D or T region of the MHC behave like immune-response genes controlling the specific antiviral immune response. Other gene(s) mapped outside the complex also affected the virus production. Both sets of genes influenced leukemia incidence, since leukemias were observed only in highly viremic strains. b) Additional non-H-2 genes, which were not involved in viremia control, were determinants in the induction of malignancies because some sensitive strains do not become leukemic despite high levels of viremia. c) The anatomical type of Moloney virus-induced leukemias varied according to the non-H-2 background. Most of the leukemias arising in B10 congeneic mice involved the thymus and were frequently limited to this organ, whereas BALB mice preferentially developed splenic leukemias. d) In a given inbred strain, the leukemias arising in different animals frequently expressed different phenotypes. It can be concluded that Moloney virus-induced leukemia is a multistep process, viral production being necessary but not sufficient in and of itself to induce a malignant transformation.     

Induction of CTL responses by simultaneous administration of liposomal peptide vaccine with anti-CD40 and anti-CTLA-4 mAb

Activation of APC via CD40-CD40 ligand pathway induces up-regulation of costimulatory molecules such as B7 and production of IL-12. Interaction between B7 on APC and CD28 on naive T cells is necessary for priming the T cells. On the other hand, interaction between B7 on APC and CTLA-4 on activated T cells transduces a negative regulatory signal to the activated T cells. In the present study, we attempted to generate tumor-specific CTL by s.c. administration of antigenic peptides encapsulated in multilamellar liposomes (liposomal peptide vaccine) with anti-CD40 mAb and/or anti-CTLA-4 mAb. Liposomal OVA257-264 and anti-CD40 mAb or anti-CTLA-4 mAb were administrated to C57BL/6 mice and the splenocytes were cocultured with OVA257-264 for 4 days. The splenic CD8+ T cells showed a significant cytotoxicity against EL4 cells transfected with cDNA of OVA. In addition, administration of both anti-CD40 and anti-CTLA-4 mAb enhanced the CTL responses. Considerable CTL responses were induced in MHC class II deficient mice by the same procedure. This finding indicated that CTL responses could be generated even in the absence of Th cells. When BALB/c mice were immunized with pRL1a peptide that are tumor-associated Ag of RLmale symbol1 leukemia cells using the same procedure, significant CTL responses were induced and prolonged survival of the BALB/c mice was observed following RLmale symbol1 inoculation. These results demonstrate that anti-CD40 mAb and anti-CTLA-4 mAb function as immunomodulators and may be applicable to specific cancer immunotherapy with antitumor peptide vaccine.     

Stimulation of the glucocorticoid-induced TNF receptor family-related receptor on CD8 T cells induces protective and high-avidity T cell responses to tumor-specific antigens

Treatment of tumor-bearing mice with a stimulatory Ab to glucocorticoid-induced TNFR family-related receptor (GITR) has previously been shown to elicit protective T cell responses against poorly immunogenic tumors. However, the role of GITR stimulation on CD8 T cells and the nature of tumor rejection Ags have yet to be determined. In this study, we show that a stimulatory mAb to GITR (clone DTA-1) acts directly on CD8 T cells, but not on CD4(+)CD25(+) regulatory T (T(reg)) cells, in B16 tumor-bearing mice to induce concomitant immunity against secondary B16 tumors, as well as protective memory following surgical excision of the primary tumor. Melanoma growth itself induced GITR expression on tumor-specific CD8 T cells, providing a mechanism whereby these cells may respond to stimulatory anti-GITR. Unexpectedly, in contrast to T(reg) cell depletion therapy with anti-CD4, GITR stimulation induced very weak CD8 T cell responses to melanocyte differentiation Ags expressed by the tumor, and did not induce autoimmune vitiligo. Accordingly, GITR-stimulated hosts that were primed with B16 melanoma rejected B16, but not the unrelated JBRH melanoma, indicating that tumor rejection Ags are tumor-specific rather than shared. In support of this, we show that GITR stimulation induces CD8 T cell responses to a tumor-specific Ag, and that these responses are of higher functional avidity compared with those induced by T(reg) cell depletion. We conclude that stimulation of GITR on effector CD8 T cells results in high-avidity T cell responses to tumor-specific Ags, thereby inducing potent antitumor immunity in the absence of autoimmunity.     

Signal transduction in lymphocytic and myeloid cells via CD24, a new member of phosphoinositol-anchored membrane molecules

The CD24 Ag is present on human B cells from the earliest stages of B lineage development and is lost on terminal B cell maturation to plasma cells. This Ag is also expressed on mature forms of granulocytes. We studied the effects of CD24 mAb on the function of both lymphocytic and myeloid cell types. We found a clear-cut increase in free cytoplasmic calcium when tonsil B cells or mononuclear cells from B cell chronic lymphatic leukemia patients were preincubated with CD24 mAb and further stimulated with goat F(ab')2 anti-mouse Ig antibodies. The same experimental setting with granulocytes instead of B lymphocytes led to the triggering of hydrogen peroxide production in these cells. CD24 Ag is expressed at higher levels on activated granulocytes and is anchored to the plasma membrane by a phosphoinositol linkage. In conclusion we provide evidence that the CD24 Ag are functional molecules in cells of different lineage, playing a signal transducing role in cell function.     

Isolation of a cDNA encoding the human CD38 (T10) molecule, a cell surface glycoprotein with an unusual discontinuous pattern of expression during lymphocyte differentiation

A cDNA clone encoding the human lymphocyte differentiation Ag CD38 was isolated from a mixture of four different lymphocyte CDNA libraries expressed transiently in COS cells and screened by panning with mAb. Transfected COS cells expressed a surface protein of Mr 46,000 that was similar to the native CD38 molecule expressed on the B cell line Daudi and the T cell leukemia HPB-ALL and which was recognized by each of the CD38 specific mAb HIT-2, T16, T168, HB7, 5D2, ICO-18, and ICO-20. The CD38 cDNA sequence predicts an unusual 30-kDa polypeptide with a short N-terminal cytoplasmic tail, and a carboxyl-terminal extracellular domain carrying the four potential N-linked glycosylation sites. The absence of significant homology with other known surface Ag including members of the Ig superfamily ruled out the possibility that CD38 was the human homologue of the murine Qa2 molecule as has been suggested previously. PvuII digests of human genomic DNA revealed a polymorphism linked to the CD38 gene.     

Identification of a novel human B cell activation antigen involved in B cell growth factor-dependent proliferation

The B6.4 mAb we present here identifies a novel activation Ag of B cell lineage. The B6.4 mAb was generated by immunizing mice with B cell growth factor (BCGF)-responding BA3 cells, and selected by its capability to block BCGF-induced proliferation of BA3 cells. The inhibitory effect of this antibody on BCGF-dependent proliferation was further confirmed by using normal activated B cells in the presence of exogenous BCGF derived from T cells or B cells. Furthermore, it did not affect IL-2-dependent proliferation of B cells. The expression of the B6.4 Ag, as analyzed by FACS, is restricted to in vitro activated B cells, and remains undetectable on resting B or T cells, PHA-activated T cells, and monocytes. The B6.4 Ag is also expressed on some lymphoblastoid B cell lines and most of the lymphomas and CLL of B cell origin; however, it did not express on pre-B cell ALL and plasma cell leukemias. The B6.4 Ag has a Mr of 35,000 Da, as determined by SDS-PAGE of radiolabeled immunoprecipitates from activated B cells. The B6.4 Ag is detectable on B cells as early as 8 h after activation, and precedes that of the IL-2R or transferrin R. All of these results suggest that the B6.4 Ag is an early activation Ag of B cells and is functionally related to a receptor of BCGF, but not IL-2.     

Antigen-binding repertoire and Ig H chain gene usage among B cell hybridomas from normal and autoimmune mice

LPS-stimulated B cells were used to generate a panel of mAb that were a random sample of the preimmune repertoire of C57BL/6 and highly autoimmune, viable motheaten mice. These mAb were tested for reactivity to a number of "self" and foreign Ag. Binding that could be detected only at nM mAb concentrations or less was considered significant. We found that a surprisingly high number of the mAb bound one or more of the Ag tested, and many mAb bound more than a single Ag. Ag-induced mAb were likewise tested and found to have greatly reduced cross-reactivities. We found no significant differences, either in frequency of Ag binding or degree of cross-reactivity, between normal and autoimmune mice. Furthermore, the frequency with which a given Ag was bound by our panel of mAb was found to be proportional to the size of the Ag. The frequency with which individual VH gene families were expressed by our panel was consistent with a stochastic usage of VH genes in the preimmune repertoire. We interpret these data as showing that the preimmune repertoire is highly cross-reactive and that the activation of autoreactive clones in autoimmune animals is due to a defect in cellular regulation rather than a difference in repertoire.     

Sequence and gene transfer analyses of HLA-CwBL18 (HLA-C blank) and HLA-Cw5 genes. Implications for the control of expression and immunogenicity of HLA-C antigens

Our previous studies suggested that a serologically undetectable HLA-C blank allele (HLA-CwBL18) is either a variant Cw5 allele or a novel HLA-C Ag. To examine these possibilities, the CwBL18 and Cw5 genes from the TCC (HLA-A1, -A2, -B52, -B18, -Cw-, -Cw-) and QBL (HLA-A26, -B18, -Cw5) EBV-transformed B lymphoblastoid cell lines (LCL) were cloned, sequenced, and transferred into HLA-A, -B, -C null LCL mutant .221 cells. The CwBL18 Ag was detected on the cell surface of CwBL18 transferents by flow cytometry with the anti-class I mAb W6/32 but not by complement-mediated cytotoxicity with currently available HLA-C specific antisera. Sequence analysis of the Cw-BL18 gene indicated that the CwBL18 Ag is "C"-like because it contains all C-locus-specific residues and amino acid replacements commonly found in HLA-C alleles. However, the amino acid sequence of the CwBL18 Ag is unusual; CwBL18 lacks unique allele-specific residues when compared with the sequences of other HLA-C alleles. Moreover, apart from the C-locus-specific differences, the sequence of CwBL18 is identical to the HLA class I consensus sequence. This striking homology of CwBL18 to other HLA class I alleles suggests that CwBL18 may be a weak Ag. Taken together, these data demonstrate that CwBL18 is not a variant Cw5 Ag but is a newly described HLA-C Ag. In contrast to CwBL18, the Cw5 Ag is serologically detectable on the cell surface of Cw5 transferents with HLA-specific allo-antisera. Rather unexpectedly, Cw5 was usually expressed at a lower level than CwBL18 on the surface of .221 transferents as evaluated by W6/32 mAb binding analyses. The sequence of Cw5 revealed several unique amino acid replacements. Two of these substitutions, at residue 35 of the alpha 1 domain and residue 275 of the transmembrane domain, may be responsible for the reduced cell surface expression of Cw5. Additional unique replacements at residues 138 and 177 of the alpha 2 domain suggest that these amino acids may be important in the formation of an epitope recognized by a Cw5-specific antibody.     

C33 antigen recognized by monoclonal antibodies inhibitory to human T cell leukemia virus type 1-induced syncytium formation is a member of a new family of transmembrane proteins including CD9, CD37, CD53, and CD63.

C33 Ag was originally identified by mAb inhibitory to syncytium formation induced by human T cell leukemia virus type 1. The Ag was shown to be a highly heterogeneous glycoprotein consisting of a 28-kDa protein and N-linked oligosaccharides ranging from 10 to 50 kDa. In the present study, cDNA clones were isolated from a human T cell cDNA expression library in Escherichia coli by using mAb C33. The identity of cDNA was verified by immunostaining and immunoprecipitation of transfected NIH3T3 cells with mAb. The cDNA contained an open reading frame of a 267-amino acid sequence which was a type III integral membrane protein of 29.6 kDa with four putative transmembrane domains and three putative N-glycosylation sites. The C33 gene was found to belong to a newly defined family of genes for membrane proteins, such as CD9, CD37, CD53, CD63, and TAPA-1, and was identical to R2, a cDNA recently isolated because of its strong up-regulation after T cell activation. Availability of mAb for C33 Ag enabled us to define its distribution in human leukocytes. C33 Ag was expressed in CD4+ T cells, CD19+ B cells, CD14+ monocytes, and CD16+ granulocytes. Its expression was low in CD8+ T cells and mostly negative in CD16+ NK cells. PHA stimulation enhanced the expression of C33 Ag in CD4+ T cells by about 5-fold and in CD8+ T cells by about 20-fold. PHA stimulation also induced the dramatic size changes in the N-linked sugars previously shown to accompany human T cell leukemia virus type 1-induced transformation of CD4+ T cells.     

Antigenic variation of Giardia lamblia in experimental human infections

To determine if Giardia surface Ag vary in human infections volunteers were inoculated enterally with trophozoites of uncloned GS/M-85 and in later experiments with two clones derived from GS/M. The surface Ag of trophozoites reisolated from 6/6 volunteers differed from the inoculum. To determine if the surface Ag of trophozoites derived from clones would also change, volunteers were inoculated with two clones, B6 or H7. B6 possesses a 200-kDa surface Ag recognized by mAb 3F6 and H7 has a 72-kDa surface Ag recognized by mAb G10/4. One of thirteen B6 and four of four H7-inoculated volunteers became infected. Analysis of Giardia obtained on day 22 from the intestines of the four H7-infected volunteers and cultures derived from these trophozoites revealed loss of the initial major surface Ag as determined by surface IFA using mAb, surface radiolabeling and loss of cytotoxicity to mAb, and Western blots. Loss of the 72-kDa Ag began after day 14 and was practically complete by day 22. The 200-kDa surface Ag was almost totally absent from the surface of Giardia isolated from the single B6-infected volunteer. Serum surface-reactive antibodies, as measured by IFA and cytotoxicity to H7 and the day 22 isolates, showed high levels of antibodies to H7, primarily to the 72-kDa surface Ag, but negligible or low levels of late-appearing antibodies to the day 22 isolates. These studies document antigenic variation of Giardia in human infections and show that humoral responses are in part isolate-specific.     

Characterization of genetic instability in radiation- and benzene-induced murine acute leukemia.

This study, using the CBA/Ca mouse as a model, compares genetic lesions associated with radiation- and benzene-induced acute leukemias. Specific types of leukemia included in the analyses are radiation-induced acute myeloid leukemia (ML), and benzene-induced lymphoblastic leukemias, lymphomas, or mix-lineage leukemias. These leukemias have histopathological characteristics similar to those seen in human acute leukemias. G-band cytogenetic analysis showed that specific deletions involving regions D-E of one copy of mouse chromosome 2 [del(2)(D-E)] were frequently associated in both radiation- and benzene-induced acute leukemias. In addition, translocations of chr2(D-E) were also observed in some cases. These results suggest an important role of chr2 (D-E) deletions and translocations in the development of radiation- and benzene-induced murine acute leukemias. Fluorescence in situ hybridization with DNA probes specific for 2(D-E), constructed in our laboratory by means of chromosomal microdissection and PCR amplification, also demonstrate 2(D-E) deletions and/or translocations in these leukemic cells. Aneuploidy of chromosomes 3, 15, 16, and Y were also frequently detected in benzene-induced leukemic cells with or without lesions on chr2. These cytogenetic findings support the previous observations that metabolites of benzene lead to spindle-fiber disruption or abnormal cytokinesis in exposed animals. In summary, genetic instabilities observed in leukemic cells isolated from mice that had developed leukemia after exposure to radiation or benzene are syntenic with those frequently detected in patients with myelodysplastic syndrome, acute ML, and acute lymphoblastic leukemia. Thus, the CBA/Ca mouse has several characteristics that make it an excellent model for the study of radiation or benzene leukemogenesis in humans.