Guidelines for resident training in veterinary clinical pathology. IV: Laboratory quality management-Teaching domains, competencies, and suggested learning outcomes

BACKGROUND

The 2019 ASVCP Education Committee Forum for Discussion, presented at the annual ASVCP/ACVP meeting, identified a need to develop recommendations for teaching laboratory quality management principles in veterinary clinical pathology residency training programs.

OBJECTIVES

To present a competency-based framework for teaching laboratory quality management principles in veterinary clinical pathology residency training programs, including entrustable professional activities (EPAs), domains of competence, individual competencies, and learning outcomes.

METHODS

A joint subcommittee of the ASVCP Quality Assurance and Laboratory Standards (QALS) and Education Committees executed this project. A draft guideline version was reviewed by the ASVCP membership and shared with selected ACVP committees in early 2022, and a final version was voted upon by the full QALS and Education Committees in late 2022.

RESULTS

Eleven domains of competence with relevant individual competencies were identified. In addition, suggested learning outcomes and resource lists were developed. Domains and individual competencies were mapped to six EPAs.

CONCLUSIONS

This guideline presents a framework for teaching principles of laboratory quality management in veterinary clinical pathology residency training programs and was designed to be comprehensive yet practical. Guidance on pedagogical terms and possible routes of implementation are included. Recommendations herein aim to improve and support resident training but may require gradual implementation, as programs phase in necessary expertise and resources. Future directions include the development of learning milestones and assessments and consideration of how recommendations intersect with the American College of Veterinary Pathologists training program accreditation and certifying examination.

Serum cobalamin concentrations in dogs infected with canine parvoviral enteritis

OBJECTIVE

To compare the serum cobalamin concentrations in canine parvovirus (CPV)-infected dogs with those of healthy control dogs.

Animals

45 dogs with CPV enteritis and 17 healthy age-matched control dogs.

Procedures

Infection was confirmed by visualization of CPV-2 through fecal electron microscopy. All dogs received supportive care. Serum samples taken at admission were used to determine cobalamin, C-reactive protein, and albumin concentrations.

Results

Serum cobalamin concentrations were significantly lower in the CPV-infected group (median [interquartile range], 173 pmol/L [< 111 to 722 pmol/L]) than in healthy control dogs (379 pmol/L [193 to > 738 pmol/L). There was no association between cobalamin concentration and C-reactive protein or albumin concentration.

Clinical Relevance

While hypocobalaminemia was common in CPV-infected dogs, the clinical relevance of this finding remains to be determined. Studies assessing markers of cellular cobalamin deficiency in dogs with CPV infection appear warranted.

Neutrophil Myeloperoxidase Index in Dogs With Babesiosis Caused by Babesia rossi

Babesiosis caused by the virulent tick-borne hemoprotozoan, Babesia rossi, results in a marked systemic inflammatory host response in dogs. Neutrophils form part of the innate immune response and contains myeloperoxidase (MPO) as the predominant component of the neutrophil lysosomal protein in azurophilic granules. The neutrophil myeloperoxidase index (MPXI), determined on the ADVIA hematology analyzer, is a quantitative estimate of intracellular MPO content. Objectives of this study were to: (a) compare MPXI in dogs with babesiosis with healthy control dogs; (b) compare MPXI in dogs that died from babesiosis with dogs that survived and controls; and (c) correlate the MPXI with the previously determined segmented and band neutrophil count and cytokine concentrations in dogs with babesiosis. Data for 140 dogs naturally infected with B. rossi and 20 healthy control dogs were retrospectively evaluated. Neutrophil counts and MPXI were determined on an ADVIA 2120 analyzer. Cytokine concentrations [interleukin (IL)-2, IL-6, IL-8, IL-10, IL-18, granulocyte-macrophage colony stimulating factor (GM-CSF), and monocyte chemo-attractant protein-1 (MCP-1)] were determined using a canine-specific multiplex immunoassay. The mortality rate of the Babesia-infected dogs was 11% (15/140). MPXI was significantly higher in Babesia-infected dogs (P = 0.033), and in Babesia-infected non-survivors (P = 0.011), compared with healthy control dogs. In Babesia-infected dogs a significant positive correlation was found between MPXI and IL-10 (r = 0.211, P = 0.039) and a significant negative correlation was found between MPXI and IL-8 (r = -0.350, P < 0.001). In Babesia-infected non-survivors, significant positive correlations were found between MPXI and IL-2 (r = 0.616, P = 0.033), IL-6 (r = 0.615, P = 0.033), IL-18 (r = 0.613, P = 0.034), GM-CSF (r = 0.630, P = 0.028), and MCP-1 (r = 0.713, P = 0.009). In Babesia-infected survivors, a significant negative correlation was found between MPXI and IL-8 (r = -0.363, P = 0.001). MPXI was correlated with pro-inflammatory cytokines in Babesia-infected dogs that died. The potential of MPXI as a novel marker of inflammation and prognosis in dogs infected with B. rossi, thus warrants further investigation.

Breed prevalence of canine lymphoma in South Africa

Lymphoma is a common haematopoietic neoplasm in dogs. Several breeds have been shown to have a predisposition to lymphoma; however, very little information exists regarding the South African dog population. This study assessed whether any breed had increased odds of developing lymphoma compared with others, and also investigated the effects of age, sex and neutering status on disease prevalence. Two study populations and their corresponding reference populations were studied retrospectively. Odds ratios (ORs) for lymphoma in 49 dog breeds, together with their 95% confidence intervals (CI), were calculated. Age effect was assessed by calculating ORs for different age categories in one of the populations. The chi-square test was used to evaluate differences in the prevalence of the various sex and neutering categories in one lymphoma population compared with its reference population. Fourteen breeds had significantly increased odds of developing lymphoma, and one breed had significantly decreased odds (p < 0.050). The median ages of the two lymphoma populations were 6.5 and 8.0 years, with the 6.1-9.0 year category having significantly increased odds of developing lymphoma (OR 1.61, CI 1.2-2.16, p = 0.002). In one of the lymphoma populations, higher proportions of males (p = 0.033) and neutered females (p = 0.006) were found when compared with the reference population. These findings suggest that certain breeds in South Africa have a higher risk of developing lymphoma, and that sex hormones may play a role in lymphoma pathogenesis. The findings may provide useful information for pet owners and veterinarians.

In-clinic laboratory diagnosis of canine babesiosis (Babesia canis canis) for veterinary practitioners in Central Europe

Objective: Haematological changes in dogs and climatic conditions favourable for the vector may assist in the quick in-house diagnosis of canine babesiosis. Material and methods: Blood samples from 358 dogs suspected to have canine babesiosis were evaluated. The diagnosis was confirmed in 113 dogs by detection of Babesia canis by microscopic examination of a stained blood smear using the concentration line technique. Results: Thrombocytopenia was present in all 113 dogs. Red blood cell count, packed cell volume and haemoglobin values were below the reference range in 62.8%, 61.1% and 46.0% of affected dogs, respectively. An increased reticulocyte count was apparent in five Babesia canis-positive dogs. Leukopenia, lymphopenia, neutropenia and monocytosis were present in 54.9%, 47.8%, 30.4% and 6.5% of the dogs, respectively. Evaluating haematological parameters by CARTanalysis revealed a predictive model (accuracy = 93.5%) for canine babesiosis, when using the leucocyte, thrombocyte, and reticulocyte count. Climatic conditions present at the most probable time of Babesia canis-infection accounted for biseasonal occurrence. Changes of climatic factors during the year influence the vector activity and in conclusion should highlight babesiosis in the ranking of differentials for veterinarians. Conclusion: The results demonstrate that a tentative diagnosis of canine babesiosis can be made based on typical haematological changes. The results recorded match well with the seasonality of the tick vector and were confirmed here by the month of sample submission.

Prognostic value of BRAF and KRAS mutation status in stage II and III microsatellite instable colon cancers

Microsatellite instability (MSI) has been associated with favourable survival in early stage colorectal cancer (CRC) compared to microsatellite stable (MSS) CRC. The BRAF V600E mutation has been associated with worse survival in MSS CRC. This mutation occurs in 40% of MSI CRC and it is unclear whether it confers worse survival in this setting. The prognostic value of KRAS mutations in both MSS and MSI CRC remains unclear. We examined the effect of BRAF and KRAS mutations on survival in stage II and III MSI colon cancer patients. BRAF exon 15 and KRAS exon 2-3 mutation status was assessed in 143 stage II (n = 85) and III (n = 58) MSI colon cancers by high resolution melting analysis and sequencing. The relation between mutation status and cancer-specific (CSS) and overall survival (OS) was analyzed using Kaplan-Meier and Cox regression analysis. BRAF V600E mutations were observed in 51% (n = 73) and KRAS mutations in 16% of cases (n = 23). Patients with double wild-type cancers (dWT; i.e., BRAF and KRAS wild-type) had a highly favourable survival with 5-year CSS of 93% (95% CI 84-100%), while patients with cancers harbouring mutations in either BRAF or KRAS, had 5-year CSS of 76% (95% CI 67-85%). In the subgroup of stage II patients with dWT cancers no cancer-specific deaths were observed. On multivariate analysis, mutation in either BRAF or KRAS vs. dWT remained significantly prognostic. Mutations in BRAF as well as KRAS should be analyzed when considering these genes as prognostic markers in MSI colon cancers.

Increased cytotoxic capacity of tumor antigen specific human T cells after in vitro stimulation with IL21 producing dendritic cells

Monocyte derived dendritic cells (moDC) electroporated with tumor associated antigen derived mRNA can elicit specific T cells against tumor cells in vivo. IL21 has been shown to enhance activation and cytotoxicity in CD8+ T cells. We therefore investigated in vitro effects on human CD8+ T-cells after stimulation with IL21 mRNA electroporated moDC. Codon modification of the IL21 gene significantly enhanced IL21 production upon electroporation of moDC. Tumor associated antigen specific CTL induction efficiency was significantly enhanced when codon modified IL21 mRNA was co-electroporated with tumor associated antigen mRNA. Tumor associated antigen specific T cells induced by codon modified IL21-DC demonstrated increased cytotoxic capacity and killing compared to control cultures. In conclusion, ectopic expression of codon modified IL21 by moDC enhances the priming efficiency of the DC as well as the cytotoxic potential of the induced CTL.

An error management system in a veterinary clinical laboratory

Error recording and management is an integral part of a clinical laboratory quality management system. Analysis and review of recorded errors lead to corrective and preventive actions through modification of existing processes and, ultimately, to quality improvement. Laboratory errors can be divided into preanalytical, analytical, and postanalytical errors depending on where in the laboratory cycle the errors occur. The purpose of the current report is to introduce an error management system in use in a veterinary diagnostic laboratory as well as to examine the amount and types of error recorded during the 8-year period from 2003 to 2010. Annual error reports generated during this period by the error recording system were reviewed, and annual error rates were calculated. In addition, errors were divided into preanalytical, analytical, postanalytical, and "other" categories, and their frequency was examined. Data were further compared to that available from human diagnostic laboratories. Finally, sigma metrics were calculated for the various error categories. Annual error rates per total number of samples ranged from 1.3% in 2003 to 0.7% in 2010. Preanalytical errors ranged from 52% to 77%, analytical from 4% to 14%, postanalytical from 9% to 21%, and other error from 6% to 19% of total errors. Sigma metrics ranged from 4.1 to 4.7. All data were comparable to that reported in human clinical laboratories. The incremental annual reduction of error shows that use of an error management system led to quality improvement.

Preclinical safety evaluation of DNA vaccines encoding modified HPV16 E6 and E7

Persistent infection with high-risk human papillomaviruses (hrHPV) can result in the formation of anogenital cancers. As hrHPV proteins E6 and E7 are required for cancer initiation and maintenance, they are ideal targets for immunotherapeutic interventions. Previously, we have described the development of DNA vaccines for the induction of HPV16 E6 and E7 specific T cell immunity. These vaccines consist of 'gene-shuffled' (SH) versions of HPV16 E6 and E7 that were fused to Tetanus Toxin Fragment C domain 1 (TTFC) and were named TTFC-E6SH and TTFC-E7SH. Gene-shuffling was performed to avoid the risk of inducing malignant transformation at the vaccination site. Here, we describe the preclinical safety evaluation of these candidate vaccines by analysis of their transforming capacity in vitro using established murine fibroblasts (NIH 3T3 cells) and primary human foreskin keratinocytes (HFKs). We demonstrate that neither ectopic expression of TTFC-E6SH and TTFC-E7SH alone or in combination enabled NIH 3T3 cells to form colonies in soft agar. In contrast, expression of HPV16 E6WT and E7WT alone or in combination resulted in effective transformation. Similarly, retroviral transduction of HFKs from three independent donors with both TTFC-E6SH and TTFC-E7SH alone or in combination did not show any signs of immortalization. In contrast, the combined expression of E6WT and E7WT induced immortalization in HFKs from all donors. Based on these results we consider it justified to proceed to clinical evaluation of DNA vaccines encoding TTFC-E6SH and TTFC-E7SH in patients with HPV16 associated (pre)malignancies.

In-clinic laboratory diagnosis of canine babesiosis (Babesia canis canis) for veterinary practitioners in Central Europe

OBJECTIVE

Haematological changes in dogs and climatic conditions favourable for the vector may assist in the quick in-house diagnosis of canine babesiosis.

MATERIAL AND METHODS

Blood samples from 358 dogs suspected to have canine babesiosis were evaluated. The diagnosis was confirmed in 113 dogs by detection of Babesia canis by microscopic examination of a stained blood smear using the concentration line technique.

RESULTS

Thrombocytopenia was present in all 113 dogs. Red blood cell count, packed cell volume and haemoglobin values were below the reference range in 62.8%, 61.1% and 46.0% of affected dogs, respectively. An increased reticulocyte count was apparent in five Babesia canis -positive dogs. Leukopenia, lymphopenia, neutropenia and monocytosis were present in 54.9%, 47.8%, 30.4% and 6.5% of the dogs, respectively. Evaluating haematological parameters by CART-analysis revealed a predictive model (accuracy= 93.5%) for canine babesiosis, when using the leucocyte, thrombocyte, and reticulocyte count. Climatic conditions present at the most probable time of Babesia canis- infection accounted for biseasonal occurrence. Changes of climatic factors during the year influence the vector activity and in conclusion should highlight babesiosis in the ranking of differentials for veterinarians.

CONCLUSION

The results demonstrate that a tentative diagnosis of canine babesiosis can be made based on typical haematological changes. The results recorded match well with the seasonality of the tick vector and were confirmed here by the month of sample submission.

Absence of Granzyme B positive tumour-infiltrating lymphocytes in primary melanoma excisional biopsies is strongly associated with the presence of sentinel lymph node metastasis

Background: Sentinel Lymph Node (SLN) status is strongly related to clinical outcome in melanoma patients. In this study we investigated the possible association between the presence of activated and/or suppressive Tumour Infiltrating Lymphocytes (TILs) and SLN status in clinically stage I/II melanoma patients.

Methods: Diagnostic primary melanoma samples from 20 patients with a sentinel lymph node metastasis were compared to melanoma samples from 20 patients with a negative sentinel lymph node, who were matched for gender, age and Breslow thickness. Presence of activated Granzyme B positive (GrB⁺) TILs, presence of suppressive (FoxP3⁺) TILs and MHC class I antigen expression on tumour cells were analysed by immunohistochemistry.

Results: FoxP3 and MHC-I expression had no direct bearing on the presence of melanoma metastases in the SLN. Whereas the presence of activated GrB⁺ TILs in the primary melanoma had no predictive value for SLN status either, their absence was strongly associated with the presence of metastasis in the SLN (p=0.001). While both GrB⁺ and FoxP3⁺ TILs could be detected in SLN metastases, a majority did not display MHC-I expression.

Conclusions: These data support a role for cytotoxic T cells in the prevention of early metastasis of melanoma to the draining lymph nodes.

Dendritic cells transfected with interleukin-12 and tumor-associated antigen messenger RNA induce high avidity cytotoxic T cells

Dendritic cells (DC) transfected with messenger RNA (mRNA) encoding tumor-associated antigens (TAA) are able to induce potent tumor-specific T-cell responses directed to a broad spectrum of tumor-associated epitopes. The in vitro generation of DC possessing all the features crucial for the induction of type 1 immune responses, such as mature state, migratory potential and interleukin-12 (IL-12p70) production is complicated. Particularly migratory potential is inversely correlated with IL-12p70 production after maturation with prostaglandin E2 (PGE2), which is included in maturation cocktails currently used in most vaccination trials. Here, we show that transfection of PGE2 matured DC with a single mRNA strain encoding for ubiquitin followed by a TAA which was linked to IL-12 by a self-cleaving 2A sequence, produced biological active IL-12p70 and were able to present the transfected TAA up to 72 h after transfection. Furthermore, use of the anti-reverse cap analog for in vitro transcription of the IL-12 mRNA enabled constitutive IL-12p70 production for up to 5 days. These transfected mature DC migrated efficiently towards lymph node derived chemokines. DCs constitutively expressing IL-12p70, generate TAA-specific cytotoxic T cells with an high functional avidity, independent of CD4+ T-cell help.

Autologous tumor cell vaccination with PF-3512676 (CPG 7909) and GM-CSF followed by subcutaneous PF-3512676 and IFN-alpha for patients with metastatic renal cell carcinoma

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Background: Metastatic renal cell carcinoma (RCC) has a poor prognosis with a 5-year survival of less than 10%. Non-specific immunotherapy, e.g. IL-2 and IFN-α achieves responses in 10–30% of patients at the cost of relatively high toxicity. Tumor vaccination has shown great promise in a variety of cancers, particularly in the adjuvant setting. Studies in metastatic setting are suitable to identify the best adjuvants and to optimize vaccination schedules. CpGs are synthetic oligonucleotides that have been shown to have superior immunogenicity in animal and human vaccination studies (Hepatitis B). Besides its positive effect on the specific immune response, CpGs also stimulate the innate immune system. We initiated a phase I/II trial to investigate the potentials of CpG in the treatment of metastatic RCC. Methods: Nephrectomized patients with progressive metastatic RCC were vaccinated with autologous tumor cells (ATC) derived from the primary tumor or metastases. Vaccines consisted of irradiated ATC, PF-3512676 and GM-CSF. The first three induction vaccinations were given weekly followed by subcutaneous administration of IFN-α (6 MIU, TIW) and PF-3512676 (8 mg bi-weekly). After 3 months tumor evaluation was performed and in case of a remission or stable disease patients continued with 3 monthly vaccinations and PF-3512676 /IFN-α. Blood was collected for immunomonitoring and DTH responses against ATC were measured before and after vaccination. Results: Preparation of vaccines was successful in 88% of the patients. Twelve patients were included and treated according to the protocol. Treatment was well tolerated. At the vaccination site we observed erythema and induration. Some patients experienced flu-like symptoms, including fever and fatigue. In all patients we observed only after vaccination a DTH response (> 10 mm) against ATC, suggestive for a specific antitumor response. Three patients (25%) achieved a partial response (durations 6, 4+, 4+ months) and 2 patients (17%) stable disease (3 months). Conclusions: This new combined immunotherapy is tolerable, safe, and immunogenic. Moreover, it can produce tumor responses in advanced RCC.

No significant financial relationships to disclose.

Changing T cell specificity by retroviral T cell receptor display

The diversity of the T cell receptor (TCR) repertoire is limited, because of the processes of positive and negative T cell selection. To obtain T cells with specificities beyond the immune system's capacity, we have developed a strategy for retroviral TCR display. In this approach, a library of T cell variants is generated in vitro and introduced into a TCR-negative murine T cell line by retroviral transfer. We document the value of TCR display by the creation of a library of an influenza A-specific TCR and the subsequent in vitro selection of TCRs that either recognize the parental influenza epitope or that have acquired a specificity for a different influenza A strain. The resulting in vitro selected TCRs induce efficient T cell activation after ligand recognition and are of equal or higher potency than the in vivo generated parent receptor. TCR display should prove a useful strategy for the generation of high-affinity tumor-specific TCRs for gene transfer purposes.

Immortalization of human CD8+ T cell clones by ectopic expression of telomerase reverse transcriptase

Replicative senescence of T cells is correlated with erosion of telomere ends. Telomerase plays a key role in maintaining telomere length. Therefore, it is thought that telomerase regulates the life span of T cells. To test this hypothesis, we have over-expressed human telomerase reverse transcriptase in human CD8(+) T cells. Ectopic expression of human telomerase reverse transcriptase led to immortalization of these T cells, without altering the phenotype and without loss of specificity or functionality. As the T cells remained dependent on cytokines and Ag stimulation for their in vitro expansion, we conclude that immortalization was achieved without malignant transformation.

NFAT-controlled expression of GFP permits visualization and isolation of antigen-stimulated primary human T cells

We have developed a new method that allows detection and isolation of viable, antigen-specific, human T cells from a heterogeneous pool of T cells. We have engineered a self-inactivating retroviral vector containing multiple (3 or 6) nuclear factor of activated T-cell (NFAT)-binding sites, followed by the minimal IL2 promoter and the reporter gene GFP. Jurkat cells, primary T-cell blasts, and T-cell clones were transduced with high efficiency (20%-40%). Stimulation of the transduced cells with phorbol myristate acetate (PMA) and ionomycin resulted in a high level expression of GFP that was maximal after 12 to 14 hours and remained stable for another 12 hours. Activation of T cells carrying the construct containing 6 NFAT-binding sites resulted in the highest mean fluorescence intensity. Cyclosporin-A and FK506 were able to block the activation-dependent GFP expression. Activation of transduced T-cell blasts with the superantigen staphylococcal enterotoxin B or of transduced antigen-specific T-cell clones with cognate antigen resulted in GFP expression. After an overnight stimulation of a heterogeneous T-cell bulk culture with an HLA mismatched stimulator cell (JY), the GFP expressing cells were cloned. As expected, the cloning frequency of the antigen-specific GFP(+) cells was considerably higher than that of the total T-cell population. Most of the T-cell clones were either cytolytic, or proliferative toward JY stimulator cells. Interestingly, we also isolated T-cell clones that were noncytolytic and nonproliferative toward JY cells, but specifically up-regulated GFP after an overnight stimulation with JY. (Blood. 2000;96:459-466)

Retargeting of a T cell line by anti MAGE-3/HLA-A2 alpha beta TCR gene transfer

BACKGROUND

The T cell receptor (TCR) is an heterodimeric protein on the cell membrane of cytotoxic T cells (CTLs). In CTLs TCRs mediate the recognition of target cells through interaction with specific, MHC class I presented peptides.

MATERIALS AND METHODS

As a model system to show proof of principle we chose the Jurkat/MA cell line and the HLA-A2.1 binding MAGE-3 derived peptide 271-279, as target specificity.

RESULTS

We show that this cell line can be successfully transduced with the dicistronic retroviral vector (LZRS) containing cDNAs encoding for the complete alpha and beta chains of the selected TCR. Following retroviral transduction, Jurkat/MA cells do express the anti-MAGE-3 TCR on their membrane. The transduced TCR is functional as travoductants are successfully triggered, upon stimulation with T2 cells or MAGE-3+ melanoma cells loaded with the MAGE-3 peptide.

CONCLUSION

We conclude that TCR gene transfer is possible and it represents a powerful therapeutic tool for the genetical modification of T calls of patients sullering from cancer.

Expression of a functional mouse-human chimeric anti-CD19 antibody in the milk of transgenic mice

Human B cell lymphomas are suitable targets for immunotherapy. Clinical trials with mouse-human chimeric B cell-specific monoclonal antibodies (mAbs) have already shown promising results. However, limitations for their use in clinical trials can be the lack of sufficient amounts and high production costs. Expression of mAbs in the mammary gland of transgenic animals provides an economically advantageous possibility for production of sufficient quantities of a promising antibody for clinical trials and beyond. In this paper, we show the feasibility of this approach, by generating transgenic mice expressing mouse-human chimeric anti-CD19 mAbs in their milk. Mouse anti-CD19 variable (V) region genes were combined with human IgG1 heavy (H) and kappa light (L) chain constant (C) region genes and fused to the bovine beta-lactoglobulin (BLG) promoter in two separate expression cassettes. Co-injection resulted in five transgenic lines. In one of these lines completely assembled chimeric mAbs were secreted into the milk, at an approximate level of 0.5 mg/ml. These mAbs were able to bind specifically to the CD19 surface antigen on human B cells.

Enrichment of an antigen-specific T cell response by retrovirally transduced human dendritic cells

The superior ability of dendritic cells (DC) in triggering antigen-specific T cell responses makes these cells attractive tools for the generation of antitumor or antiviral immunity. We report here an efficient retroviral transduction system for the introduction of antigens into DC. A retroviral vector encoding several CTL epitopes in a string-of-beads fashion in combination with the marker gene green fluorescence protein (GFP) was generated. Polyepitope transduced EBV-LCL could be isolated on the basis of GFP expression and were found to be sensitive to lysis by antigen-specific cytotoxic T cells, demonstrating that antigens encoded by the retroviral construct were stably expressed, processed, and presented in the context of HLA class I molecules. CD34(+) cells isolated from G-CSF mobilized peripheral blood were transduced with high efficiency (40-60%) with this retroviral construct. These cells could be considerably expanded in vitro and differentiated into mature DC without loss of the transduced antigen. DC transduced with the polyepitope constructs were able to mount a CTL response against an influenza epitope in the context of HLA-A2, demonstrating the antigen-specific CTL priming capacity of retrovirally transduced DC. Staining of the T cells with tetramers of HLA-A2 and the influenza virus peptide demonstrated a marked antigen-specific CTL enrichment after 2 in vitro stimulations using DC transduced with the polyepitope. However, additional in vitro stimulations of the T cells with transduced DC did not result in a further enrichment of tetramer staining cells.

Construction and characterization of a fusion protein of single-chain anti-CD20 antibody and human beta-glucuronidase for antibody-directed enzyme prodrug therapy

The CD20 antigen is an attractive target for specific treatment of B-cell lymphoma. Antibody-directed enzyme prodrug therapy (ADEPT) aims at the specific activation of a nontoxic prodrug at the tumor site by an enzyme targeted by a tumor-specific antibody such as anti-CD20. We constructed a fusion protein of the single-chain Fv anti-CD20 mouse monoclonal antibody (MoAb) 1H4 and human beta-glucuronidase for the activation of the nontoxic prodrug N-[4-doxorubicin-N-carbonyl(-oxymethyl) phenyl] O-beta-glucuronyl carbamate to doxorubicin at the tumor site. The cDNAs encoding the light- and heavy-chain variable regions of 1H4 were cloned, joined by a synthetic sequence encoding a 15-amino acid linker and fused to human beta-glucuronidase by a synthetic sequence encoding a 6-amino acid linker. An antibody-enzyme fusion protein-producing cell line was established by transfection of the construct into human embryonic kidney 293/EBNA cells. The yield of active fusion protein was 100 ng/mL transfectoma supernatant. Antibody affinity, antibody specificity, and enzyme activity were fully retained by the fusion protein. Immunoprecipitation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the fusion protein has a relative molecular weight (Mw) of 100 kD under denaturing conditions. Gel filtration analysis indicated that the enzymatically active form of the fusion protein is a tetramer with an Mw of approximately 400 kD. The nontoxic prodrug N-[4-doxorubicin-N-carbonyl(-oxymethyl) phenyl] O-beta-glucuronyl carbamate was hydrolyzed by the fusion protein at a hydrolysis rate similar to that of human beta-glucuronidase. When the fusion protein was specifically bound to Daudi lymphoma cells, the prodrug induced similar antiproliferative effects as doxorubicin. Thus, it is feasible to construct a eukaryotic fusion protein consisting of a single-chain anti-CD20 antibody and human beta-glucuronidase for future use in the activation of anticancer prodrugs in B-cell lymphoma.

Lysis of syngeneic tumor B cells by autoreactive cytotoxic T lymphocytes specific for a CD19 antigen-derived synthetic peptide

Cytotoxic T lymphocytes (CTL) play an important role in the destruction of immunogenic tumors. A novel category of target antigens for CTL concerns normal differentiation antigens as most clearly demonstrated in human melanoma. In the case of B-cell cancers, differentiation antigens normally expressed on B cells may be useful targets. In this report, we have focused on the murine B-cell differentiation antigens CD19 and CD20. We have identified 18 peptide sequences on the basis of major histocompatibility complex (MHC) class-I binding-motifs as candidates for the induction of autoreactive CTL. Six of the peptides were capable of binding efficiently to either Kb or Db and were subsequently used for in vivo induction of CTL. Vaccination with each of three peptides led to peptide-specific CTL. Two peptides were derived from the mCD20 antigen and one from the mCD19 antigen. CTL specific for the mCD19-derived peptide were also capable of killing a syngeneic B-cell tumor line. Recognition of the peptide as well as the tumor cells was shown to be Kb restricted. This is the first report to show that autoreactive CTL recognizing peptides derived from B-cell-specific differentiation antigens can be generated by vaccination with a synthetic peptide.

Characterization of a series of isotype switch variants of a new CD20 monoclonal antibody

A series of heavy chain switch variants has been isolated from a new B cell-specific monoclonal antibody belonging in the CD20 cluster. The antibodies NKI-B20/1, NKI-B20/2b, and NKI-B20/2a (of isotype IgG1, IgG2b, and IgG2a, respectively) have been used to study the influence of isotype and of the target antigen on the capacity to mediate cytotoxicity with a number of effector mechanisms. Unlike many mouse MAbs, NKI-B20/2b and NKI-B20/2a were cytolytic with human complement on human target cells that did not express the complement regulatory factor HRF20. All 3 isotypes of NKI-B20 mediated antibody-dependent cell-mediated cytotoxicity (ADCC) with rIL-2-activated NK cells from mouse spleen. Here the antigen density seemed the most important factor in determining the level of cell kill. With mouse peritoneal macrophages as effector cells again all 3 isotypes of NKI-B20 mediated cytotoxicity. For the IgG1 and IgG2b variants of NKI-B20 this is at variance to what has been reported for MAbs of other specificities. Despite the high activity with murine effector cells none of the NKI-B20 MAbs mediated ADCC with human peripheral blood NK cells, with or without stimulation with rIL-2, due to the lack of interaction of the murine MAbs with the human Fc receptor. The CD20 antigen appears to be a good target antigen for various forms of cytotoxicity, to which its relatively high antigenic density, its resistance to antibody-induced modulation, and its unusual structure all contribute.

Eradication of large human B cell tumors in nude mice with unconjugated CD20 monoclonal antibodies and interleukin 2

Since antibody-dependent cellular cytotoxicity is considered an important mechanism by which mAbs may exert their antitumor effects, it seems likely that these antitumor effects can be enhanced by the activation of the appropriate effector cell populations. We have used nude mice xenografted with human Daudi tumor cells as a model to compare the antilymphoma effects of unconjugated CD19 (CLB-CD19) and CD20 (BCA-B20) mAbs (IgG2a subclass) alone or in combination with recombinant human interleukin 2 (rhIL-2) or recombinant mouse granulocyte-macrophage-colony-stimulating factor (rmGM-CSF). Treatment of established tumors with BCA-B20 or rhIL-2 or rmGM-CSF as a single agent, all resulted in highly significant decreases of tumor growth rates, but did not increase the number of complete regressions. The combination of CLB-CD19 or BCA-B20 mAbs with rhIL-2 or rmGM-CSF resulted in larger decreases of growth rates than either of the agents alone. Complete eradication of large Daudi tumors could be achieved when treatment with BCA-B20 mAbs was combined with rhIL-2, but not with the combination of CLB-CD19 mAbs and rhIL-2 nor with the combination of BCA-B20 mAbs and rmGM-CSF. Cured animals kept for 2-3 months after complete regression of the tumors were still tumor free. Regression of tumors was correlated with the infiltration of lymphocytes as well as macrophages into the tumor. This is the first report to show that unconjugated CD20 mAbs are to be preferred over unconjugated CD19 mAbs, and interleukin 2 over GM-CSF in the combinational treatment of large B cell tumors.

Integration vectors for antibody chimerization by homologous recombination in hybridoma cells

Gene targeting in hybridoma cells provides a tool for generating chimeric antibodies with great ease and at high yield. We present an evaluation of integration vectors for the chimerization of the immunoglobulin heavy chain locus which are universally applicable to hybridomas of different isotypes and mouse strains. There are three problems arising with vector integration: (i) the frequent persistence of the parental isotype; (ii) an isotype-dependent aberrant replacement-like recombination giving rise to antibodies devoid of the CH1 domain; and (iii) secondary recombinations leading to excision of the integrated sequence. To overcome these problems, we have systematically evaluated the consequences of extending the vector flank. Although the homology length clearly determines the recombination frequency, this effect is counteracted by the secondary recombination, which also correlates to the homology length. In contrast, the truncating recombination events are not dependent on the homology length and never lead to re-excision of the construct. To take advantage of the increased genetic stability obtained with short flanks, we constructed an enrichment vector which yields high recombination efficiencies despite using a short flanking sequence. In addition, irradiation of the cells enhanced homologous recombination. The problem of the co-production of two isotypes was overcome by a two-step targeting reaction.

Enhanced antitumor effects of CD20 over CD19 monoclonal antibodies in a nude mouse xenograft model

We used a nude mouse xenograft tumor model to compare the efficacy of unconjugated CD19 and CD20 mAbs (IgG2a subclass) in mediating antilymphoma effects. Treatment with the CD20 mAbs NKI-B20 and BCA-B20 resulted in a drastic decrease in tumor take rate (P < 0.0001) in comparison to controls, whereas the CD19 mAb CLB-CD19 was ineffective. Tumor growth rates were reduced by both CD19 and CD20 (P < 0.0001). The decrease in growth rate induced by NKI-B20 or BCA-B20 was larger than that induced by CLB-CD19 (P = 0.0022). In vitro experiments showed that NKI-B20 or BCA-B20 are more powerful than CLB-CD19 in mediating lysis by interleukin 2-activated natural killer cells. No difference was observed between different isotypes (IgG1, IgG2a, IgG2b) of the switch variants of NKI-B20 or CLB-CD19. A positive correlation between antigen density and the sensitivity to antibody-dependent cellular cytotoxicity was demonstrated with human lymphoblastoid B cells, JY, transfected with cDNA encoding the human CD19 antigen that expressed high levels of this antigen. These cells are more efficiently killed by natural killer cells when coated with CLB-CD19 mAbs than JY wildtype cells that express 1 log lower levels of the CD19 antigen. Antibody-dependent cellular cytotoxicity experiments with thioglycolate-activated macrophages show a more complex relationship between antigen density, isotype of the mAb, and cytotoxicity. BCA-B20 (IgG2a) and CLB-CD19 (IgG2a) and all isotypes of NKI-B20 mediated strong cytotoxicity, whereas CLB-CD19 isotypes IgG1 and IgG2b were associated with limited cytotoxicity. Proliferation of Daudi cells was inhibited with high concentrations of all isotypes of CLB-CD19, but not with any of the CD20 mAbs. To our knowledge this is the first report showing that the antitumor effects in vivo of unconjugated CD20 mAbs are far superior to those of CD19 mAbs.