Effective Systemic Immune Responses Research Articles

Tumor Microenvironment Regulation and Cancer Targeting Therapy Based on Nanoparticles.

Although we have made remarkable achievements in cancer awareness and medical technology, there are still tremendous increases in cancer incidence and mortality. However, most anti-tumor strategies, including immunotherapy, show low efficiency in clinical application. More and more evidence suggest that this low efficacy may be closely related to the immunosuppression of the tumor microenvironment (TME). The TME plays a significant role in tumorigenesis, development, and metastasis. Therefore, it is necessary to regulate the TME during antitumor therapy. Several strategies are developing to regulate the TME as inhibiting tumor angiogenesis, reversing tumor associated macrophage (TAM) phenotype, removing T cell immunosuppression, and so on. Among them, nanotechnology shows great potential for delivering regulators into TME, which further enhance the antitumor therapy efficacy. Properly designed nanomaterials can carry regulators and/or therapeutic agents to eligible locations or cells to trigger specific immune response and further kill tumor cells. Specifically, the designed nanoparticles could not only directly reverse the primary TME immunosuppression, but also induce effective systemic immune response, which would prevent niche formation before metastasis and inhibit tumor recurrence. In this review, we summarized the development of nanoparticles (NPs) for anti-cancer therapy, TME regulation, and tumor metastasis inhibition. We also discussed the prospect and potential of nanocarriers for cancer therapy.

Hydrogel/nanoparticles-mediated cooperative combination of antiangiogenesis and immunotherapy

Vascular abnormalities are directly related to the tumor immunosuppressive microenvironment, which is an important obstacle to effective immunotherapy. The combination of antiangiogenesis therapy and immunotherapy may promote a mutually reinforcing cycle of immune reprogramming and vascular normalization to increase the effectiveness of immunotherapy. Herein, a hydrogel/nanosystem-mediated antiangiogenesis combined immunotherapy strategy was used to regulate the tumor microenvironment by the controlled release of apatinib, CD47 antibody (aCD47), and CpG. The combination of hydrogel with nanoparticles protected drug activity and maintained a long-term slow release of the drug for maximum synergistic efficacy. Apatinib promotes vascular normalization in tumors and enhances the efficacy of aCD47-based immunotherapy. The addition of immunoadjuvant CpG further enhanced antigen presentation and stimulated the anti-tumor activity of macrophages to strengthen the efficacy of antiangiogenesis combined immunotherapy. The main effector immune cells, including CD4+ T, CD8+ T, NK, and activity DCs, were significantly increased after combination treatment, while the proportion of various immunosuppressive cells decreased significantly, especially MDSCs and M2-polarized macrophages. Based on an effective systemic immune response, the hydrogel/nanoparticle-mediated cooperative combination of antiangiogenesis and immunotherapy enhanced the synergistic effect for primary tumors and prevented metastasis for tumor treatment. The biomaterial-mediated antiangiogenesis combined immunotherapy strategy is a promising strategy for effective immunotherapy. Statement of significanceRelieving immunosuppression of the tumor microenvironment is the key to restoring and rebuilding the normal anti-tumor immune defense of the body. Vascular abnormalities are directly related to the tumor immunosuppressive microenvironment, which is an important obstacle to effective immunotherapy. The combination of antiangiogenesis and immunotherapy may promote a mutually reinforcing cycle of immune reprogramming and vascular normalization to increase the effectiveness of immunotherapy. For the combination of antiangiogenesis and immunotherapy, effective drug delivery to overcome local immune tolerance and regulate the tumor microenvironment to increase therapeutic effects is an important issue. The hydrogel/nanomaterial composite system constructs a dual sustained-release system to achieve step-by-step controlled release of antiangiogenic drugs and immune immunotherapy drugs to promote cooperative combination therapy.

Is there a link between very early changes of primary and secondary lymphoid organs in 18F-FDG-PET/MRI and treatment response to checkpoint inhibitor therapy?

Response assessment or prediction to checkpoint inhibitor therapy (CIT) is an unsolved problem in current routine diagnostics of patients with melanoma. Here, we evaluated very early changes of primary and secondary lymphoid organs under CIT in multiparametric [18F]-labeled fluorodeoxyglucose-positron emission tomography (18F-FDG-PET)/MRI as possible predictors of treatment response and investigated their correlation with baseline blood immune biomarkers. Between October 2014 and November 2017, 17 patients with unresectable melanoma (8 females; 65±11 years) undergoing CIT were prospectively evaluated using whole-body 18F-FDG-PET/MRI before CIT start (t0), 2 weeks (t1) and 3 months after CIT initiation (t2). At each time point, the volume, the 18F-FDG-uptake and the mean apparent diffusion coefficient (ADC) of the spleen as well as the 18F-FDG uptake of the bone marrow were assessed. Relative lymphocyte count (RLC), relative eosinophil count (REC) and neutrophil-lymphocyte ratio (NLR) were assessed at baseline. Response Evaluation Criteria in Solid Tumours modified for immune-based therapeutics (iRECIST) and decisions from an interdisciplinary tumor board were used for treatment response evaluation at t2. iRECIST was compared with PET response criteria in solid tumors for image-based response evaluation at different time points. Comparative analysis was conducted with Mann-Whitney U test with false discovery rate correction for multiple testing and correlation coefficients were computed. In lymphoid organs, significant differences (p<0.05) between responders (9/17) and non-responders were found for the 18F-FDG-uptake in the spleen at t1 and the increase of the uptake t1-t0 (responders/non-responders: standardized uptake value lean body mass 1.19/0.93; +49%/−1%). The best correlation coefficients to baseline biomarkers were found for the 18F-FDG-uptake in the spleen at t1: NLR, r=−0.46; RLC, r=0.43; REC, r=0.58 (p<0.05), respectively. Compared with the non-responder group, the responder group showed marked increases also in the volume of the spleen (+22%/+10%), the 18F-FDG-uptake of bone marrow (+31%/−9%) at t1 and the ADCmean at t2 (+46%/+15%) compared with t0, however, not reaching significance. Our findings indicate that an effective systemic immune response in patients undergoing CIT can be detected as a significantly increased spleen activity in 18F-FDG-PET as early as 2 weeks after treatment initiation.Trial registration number NCT03132090, DRKS00013925.

Comparison of oral and nasal immunization with inactivated porcine epidemic diarrhea virus on intestinal immunity in piglets.

Porcine epidemic diarrhea virus (PEDV) has proven to be a major problem for the porcine industry worldwide. Conventional injectable vaccines induce effective systemic immune responses but are less effective in preventing PEDV at mucosal invasion sites, including the nasal or oral mucosa. Additionally, antigens delivered orally are easily degraded. Nasal immunization induces intestinal mucosal immune responses, which can aid in blocking viral invasion, and requires fewer antigen inoculation doses. Therefore, nasal immunizations are considered to be a potential approach to overcome viral infections. In the present study, nasal immunization of piglets was performed using inactivated PEDV combined with Bacillus subtilis as an immunopotentiator and the efficacy of nasal immunization was assessed. The results demonstrated that compared with oral immunization, piglets from the nasal immunization group exhibited higher levels of neutralizing antibodies (P<0.01) in the intestine, PEDV-specific immunoglobulin (Ig)G (P<0.01) in serum and PEDV-specific secretory IgA (SIgA) in saliva (P<0.01) and nasal secretions (P<0.01). An increased number of intestinal CD3+ T cells, IgA-secreting cells and intraepithelial lymphocytes (P<0.05) were also observed. Furthermore, the protein expression levels of interleukin-6 and interferon-γ, relative to the control PEDV infection, were also significantly elevated (P<0.05). The results of the present study indicate that nasal immunization is more effective at inducing the intestinal mucosal immune response, and provide new insights into a novel vaccination strategy that may be used to decrease the incidence of PEDV infections.

Oral administration of lipopolysaccharides from Escherichia coli (serotype O111:B4) does not induce an effective systemic immune response in milk-fed Holstein calves

It is well established that intravenous administration of lipopolysaccharides (LPS)-cell wall components from gram-negative bacteria-induce acute inflammatory responses in dairy calves, but the effect of oral administration of LPS to dairy calves is currently unknown. To evaluate the effects of oral administration of LPS derived from Escherichia coli (serotype O111:B4) on innate immune responses in milk-fed Holstein calves, 20 visually healthy calves (34 ± 1 d) received 4 L of milk with LPS (12 μg/kg body weight; n = 10; LPS) or without LPS (n = 10; control) at the morning feeding. Samples were collected at 0.5 h before the morning feeding and at 3, 6, 24, 48, 72, and 168 h after the morning feeding to measure rectal temperature and heart rate, as well as plasma-negative and plasma-positive acute phase proteins (i.e., haptoglobin, serum amyloid A, albumin, total protein, and fibrinogen) and immunoglobulin concentrations (IgG, IgM, and IgA). None of these measurements was affected by the oral administration of LPS. Oral administration of LPS at 12 μg/kg of body weight did not induce an acute inflammatory response in visually healthy milk-fed Holstein calves when administered in milk.

Administration of Dendritic Cells and Anti-PD-1 Antibody Converts X-ray Irradiated Tumors Into Effective In situ Vaccines

Danger signals and release of tumor-specific antigens after exposure to ionizing radiation can convert an irradiated tumor into an in situ vaccine. However, radiation alone is not sufficient to induce an effective systemic immune response. In this study, we investigated whether a combination of x-ray irradiation with bone marrow-derived dendritic cells (BM-DCs) and anti-PD-1 antibody (αPD1-ab) administration can enhance both local tumor control and the systemic abscopal effect in murine subcutaneous tumor models. B16/BL6 melanoma and Lewis lung carcinoma cells were examined for radiosensitivity and expression of H-2kd and PD-L1 before and after irradiation. The tumor cells were implanted subcutaneously in the left thigh of C57BL/6 mice as primary tumors. BM-DCs were induced from mouse bone marrow cells using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The primary tumors were treated with 8Gy of x-ray, followed by simultaneous intratumoral injection of BM-DCs and intraperitoneal injection of αPD1-ab. To examine the abscopal effect, the same tumor cells were also inoculated in the right thigh as metastatic tumors 4days after the primary tumor inoculation, and only the primary tumors were treated with the same protocols. Invivo analyses of tumor growth and survival rates and in vitro analyses of splenic T-cell proliferation and interferon-γ release were performed. The triple-combination treatment of x-ray irradiation with BM-DC and αPD1-ab administration inhibited primary tumor growth and significantly extended survival time in association with significant increase of T-cell proliferation and interferon-γ release. In addition, this triple-combination treatment significantly inhibited the growth of metastatic tumors. The results indicated that BM-DC and αPD1-ab administration led to the conversion of irradiated tumors into effective in situ vaccines. This combination therapy can be a promising approach to develop a novel individualized therapy for patients with solid cancers.

M CELLS ARE THE IMPORTANT POST IN THE INITIATION OF IMMUNE RESPONSE IN INTESTINE

Microfold cells (M cells) are specialized intestinal epithelial cells that initiate mucosal immune responses. These unique phagocytic epithelial cells are specialized for the transfer of a broad range of particulate antigens and microorganisms across the follicle-associated epithelium (FAE) into the gut-associated lymphoid tissue (GALT) by a process termed transcytosis. The molecular basis of antigen uptake by M cells has been gradually identified in the last decade. Active sampling of intestinal antigen initiates regulated immune responses that ensure intestinal homeostasis. The delivery of luminal substances across the intestinal epithelium to the immune system is a critical event in immune surveillance resulting in tolerance to dietary antigens and immunity to pathogens (e.g., bacteria, viruses, and parasites) and their toxins. Several specialized mechanisms transport luminal antigen across the gut epithelium. Discovery of M cell-specific receptors are of great interest, which could act as molecular tags for targeted delivery oral vaccine to M cells. Recent studies demonstrated that M cells utilize several receptors to recognize and transport specific luminal antigens. Vaccination through the mucosal immune system can induce effective systemic immune responses simultaneously with mucosal immunity. How this process is regulated is largely unknown. This review aims to show a new understanding of the factors that influence the development and function of M cells; to show the molecules expressed on M cells which appear to be used as immunosurveillance receptors to sample pathogenic microorganisms in the gut; to note how certain pathogens appear to exploit M cells to inject the host; and, finally, how this knowledge is used to specifically "target" antigens to M cells to attempt to improve the efficacy of mucosal vaccines. Recently, substantial progress has been made in our understanding of the factors that influence the development and function of M cells.

Distinct immune signatures in directly treated and distant tumors result from TLR adjuvants and focal ablation.

Both adjuvants and focal ablation can alter the local innate immune system and trigger a highly effective systemic response. Our goal is to determine the impact of these treatments on directly treated and distant disease and the mechanisms for the enhanced response obtained by combinatorial treatments.Methods: We combined RNA-sequencing, flow cytometry and TCR-sequencing to dissect the impact of immunotherapy and of immunotherapy combined with ablation on local and systemic immune components.Results: With administration of a toll-like receptor agonist agonist (CpG) alone or CpG combined with same-site ablation, we found dramatic differences between the local and distant tumor environments, where the directly treated tumors were skewed to high expression of F4/80, Cd11b and Tnf and the distant tumors to enhanced Cd11c, Cd3 and Ifng. When ablation was added to immunotherapy, 100% (n=20/20) of directly treated tumors and 90% (n=18/20) of distant tumors were responsive. Comparing the combined ablation-immunotherapy treatment to immunotherapy alone, we find three major mechanistic differences. First, while ablation alone enhanced intratumoral antigen cross-presentation (up to ~8% of CD45+ cells), systemic cross-presentation of tumor antigen remained low. Combining same-site ablation with CpG amplified cross-presentation in the draining lymph node (~16% of CD45+ cells) compared to the ablation-only (~0.1% of CD45+ cells) and immunotherapy-only cohorts (~10% of CD45+ cells). Macrophages and DCs process and present this antigen to CD8+ T-cells, increasing the number of unique T-cell receptor rearrangements in distant tumors. Second, type I interferon (IFN) release from tumor cells increased with the ablation-immunotherapy treatment as compared with ablation or immunotherapy alone. Type I IFN release is synergistic with toll-like receptor activation in enhancing cytokine and chemokine expression. Expression of genes associated with T-cell activation and stimulation (Eomes, Prf1 and Icos) was 27, 56 and 89-fold higher with ablation-immunotherapy treatment as compared to the no-treatment controls (and 12, 32 and 60-fold higher for immunotherapy-only treatment as compared to the no-treatment controls). Third, we found that the ablation-immunotherapy treatment polarized macrophages and dendritic cells towards a CD169 subset systemically, where CD169+ macrophages are an IFN-enhanced subpopulation associated with dead-cell antigen presentation.Conclusion: While the local and distant responses are distinct, CpG combined with ablative focal therapy drives a highly effective systemic immune response.

A novel immunization strategy using cytokine/chemokines induces new effective systemic immune responses, and frequent complete regressions of human metastatic melanoma

ABSTRACTImmune responses have been elicited by a variety of cancer vaccines, but seldom induce regressions of established cancers in humans. As a novel therapeutic immunization strategy, we tested the hypothesis that multiple cytokines/chemokines secreted early in secondary responses ex-vivo might mimic the secretory environment guiding new immune responses. The early development of immune responses is regulated by multiple cytokines/chemokines acting together, which at physiologic concentrations act locally in concert with antigen to have non-specific effects on adjacent cells, including the maturation of dendritic cells, homing and retention of T cells at the site of antigen, and the differentiation and expansion of T cell clones with appropriate receptors. We postulated that repeated injections into a metastasis of an exogenous chemokine/cytokine mixture might establish the environment of an immune response and allow circulating T cell clones to self- select for mutant neo-epitopes in the tumor and generate systemic immune responses. To test this idea we injected some metastases in patients with multiple cutaneous melanoma nodules while never injecting other control metastases in the same patient. New immune responses were identified by the development of dense lymphocytic infiltrates in never-injected metastases, and the frequent complete regression of never-injected metastases, a surprising observation. 70% of subjects developed dense infiltrates of cytotoxic CD8 cells in the center and margin of never-injected metastases; 38% of subjects had complete and often durable regressions of all metastases, without the use of check-point inhibitors, suggesting that, as a proof-of-principle, an immunization strategy can control advanced human metastatic melanoma.

Adoptive transfer of immunity against red mouth disease in rainbow trout (Oncorhynchus mykiss)

Enteric Red Mouth Disease (ERM) caused by Yersinia ruckeri is among the bacterial diseases in rainbow trout aquaculture that can be controlled by registered vaccines and part of these vaccines can be delivered by immersion which is the most convenient way of application inducing good antibody responses and ensuring decreased handling costs. However, the mechanisms by which fish are protected against Yersinia ruckeri are unclear. To shed light on this question we have bath vaccinated clonal rainbow trout donors by using a commercially available vaccine, and leukocytes have been isolated from vaccinated donors followed by adoptive cell transfer to naive fish recipients of the same trout clone. Control recipients were injected with same numbers of leukocytes from non-vaccinated clonal donors. Transfer between genetically identical donors and recipients ensured that immune cells were not rejected by the recipients. After transfer, both groups of recipients were bath infected with a virulent field strain of Yersinia ruckeri. While rainbow trout that have received leukocytes from vaccinated donors showed no mortality, less than 40% of control recipients survived the challenge. Flow cytometry using leukocytes from recipient survivors revealed that the percentage of IgM B cells was considerably higher in recipients that were injected with leukocytes from vaccinated donors when compared with control recipients, while no differences in the percentages of CD8 cells among groups were recorded. Being the first report on adoptive cellular transfer of immunity in a bacterial infection in fish these data suggest that immunity was rather transferred by IgM B cells, but not by CD8 cytotoxic T cells. . It can be further suggested that bath vaccination has caused an effective systemic immune response since protection could be transferred by non-mucosal leukocytes.

Abstract A038: The feasibility of inducing effective systemic immune responses to human metastatic melanoma with intralesional secreted cytokines

Abstract The induction of new additional immune responses to potential neoantigens on metastatic melanoma resulting in dense lymphocytic infiltrates might cause regression of metastases and could enhance the effects of anti-check point therapies. The blocking of CTLA-4 or PD-1/PD-L1, which normally constrain immune responses, results in significant prolongation of life and up to 7% complete responses (CRs) of metastatic melanoma when used individually. Insufficient nascent anti-melanoma immunity may account for the relatively low frequency of CRs. Also the lack of specificity in the dis-inhibition of immune responses can cause adverse reactions. We investigated a different strategy: inducing new specific immune responses to metastatic melanoma with mixed secreted cytokines. The development of immune responses is regulated by multiple cytokines/chemokines (CKs) acting in concert. To mimic this secretory environment, in a non-randomized prospective study, 88 patients with multiple palpable cutaneous/subcutaneous metastases (stages IIIC and IV-M1a) received weekly injections of autologous secreted CKs into some metastatic nodules while other metastases were never injected. CKs were prepared ex-vivo by stimulating PBMCs with recall microbial antigens to which the patients were sensitive as assessed by PBMC proliferative responses. The secreted mixtures contained individual cytokines at picogram to nanogram concentrations. New immune responses were identified by the development of dense lymphocytic infiltrates in never-injected metastases, consisting of CD8 and smaller numbers of CD4 T cells. This study was conducted before the availability of current therapies. After multiple injections into some metastatic nodules, never-injected metastases developed dense tumor-infiltrating lymphocytes (TILs) and often regressed completely. CD8 TILs from metastases directly killed fresh autologous melanoma cells ex-vivo in an MHC-restricted manner without in- vitro boosting. Although both never-injected and injected metastases often regressed completely, in some patients new metastases appeared even while never- injected nodules were regressing. The new metastases often regressed with or without injections. In 40% of subjects all never-injected and injected metastases regressed completely for &amp;gt; 2 months. 20% remained free of disease for 5 to 28 years (median 60 months, range 2 to 334 months). Median overall survival of patients, progressing and regressing, was 28.5 months (4-348 months), with 55% of patients surviving 2 years, and 30% 5 years. Durable disease-free survival also occurred in recipients of intracutaneous CKs mixed with irradiated autologous melanoma cells. No adverse events occurred. We conclude that intralesional secreted, mixed CKs can induce new systemic and effective cellular immune responses to metastatic melanoma. Mixtures of secreted cytokine/chemokines (CKs) may be more effective in inducing the development of immune responses than individual CKs. These immune responses were associated with a surprisingly high frequency (40%) of complete regressions and prolonged disease-free periods of 1 to 28 years. These new anti-melanoma cellular immune responses also might enhance the frequency of clinical responses to subsequent anti-check point therapies. Citation Format: Fred T. Valentine, Frederick M. Golomb, Matthew Haris, Daniel F. Roses. The feasibility of inducing effective systemic immune responses to human metastatic melanoma with intralesional secreted cytokines. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A038.

Immunization of Aged Pigs with Attenuated Pseudorabies Virus Vaccine Combined with CpG Oligodeoxynucleotide Restores Defective Th1 Immune Responses

Background and AimsAttempts to immunize aged subjects often result in the failure to elicit a protective immune response. Murine model studies have shown that oligonucleotides containing CpG motifs (CpG ODN) can stimulate immune system in aged mice as effectively as in young mice. Since many physiological and pathophysiological data of pigs can be transferred to humans, research in pigs is important to confirm murine data. Here we investigated whether immunization of aged pig model with attenuated pseudorabies virus vaccine (PRV vaccine) formulated with CpG ODN could promote a successful development of immune responses that were comparable to those induced in young pigs in a similar manner.MethodologyYoung and aged pigs were immunized IM with PRV vaccine alone, or in combination with CpG ODN respectively. At days 3, 7, 14 post immunization sera were assayed by ELISA for IgG titres, at day 7 for IgG1 and IgG2 subtypes titres. All blood samples collected in evacuated test tubes with K-EDTA at day 7 were analyzed for flow cytometer assay. Blood samples at day 7 collected in evacuated test tubes with heparin were analysed for antigen-specific cytokines production and peripheral blood mononuclear cells (PBMCs) proliferative responses.ResultsCpG ODN could enhance Th1 responses (PRV-specific IgG2/IgG1 ratio, proliferative responses, Th1 cytokines production) when used as an adjuvant for the vaccination of aged pigs, which were correlated with enhanced CD4+ T cells percentage, decreased CD4+CD8+CD45RO+ T cells percentage and improved PRV-specific CD4+ T cells activation.ConclusionsOur results demonstrate a utility for CpG ODN, as a safe vaccine adjuvant for promoting effective systemic immune responses in aged pig model. This agent could have important clinical uses in overcoming some of age-associated depressions in immune function that occur in response to vaccination.

Mucosal Immune System and M Cell-targeting Strategies for Oral Mucosal Vaccination

Vaccination is one of the most effective methods available to prevent infectious diseases. Mucosa, which are exposed to heavy loads of commensal and pathogenic microorganisms, are one of the first areas where infections are established, and therefore have frontline status in immunity, making mucosa ideal sites for vaccine application. Moreover, vaccination through the mucosal immune system could induce effective systemic immune responses together with mucosal immunity in contrast to parenteral vaccination, which is a poor inducer of effective immunity at mucosal surfaces. Among mucosal vaccines, oral mucosal vaccines have the advantages of ease and low cost of vaccine administration. The oral mucosal immune system, however, is generally recognized as poorly immunogenic due to the frequent induction of tolerance against orally-introduced antigens. Consequently, a prerequisite for successful mucosal vaccination is that the orally introduced antigen should be transported across the mucosal surface into the mucosa-associated lymphoid tissue (MALT). In particular, M cells are responsible for antigen uptake into MALT, and the rapid and effective transcytotic activity of M cells makes them an attractive target for mucosal vaccine delivery, although simple transport of the antigen into M cells does not guarantee the induction of specific immune responses. Consequently, development of mucosal vaccine adjuvants based on an understanding of the biology of M cells has attracted much research interest. Here, we review the characteristics of the oral mucosal immune system and delineate strategies to design effective oral mucosal vaccines with an emphasis on mucosal vaccine adjuvants.

Gene therapy for lung cancer

Lung cancer is a leading cause of cancer death and standard chemotherapies are resulting in only marginal improvements in outcome. Experimental approaches involving gene therapy are attractive in this clinical setting. There are two basic types of genes utilized, either those intended to induce immunity or those that are directly tumoricidal. Immunity-inducing genes that have been used in model (and some human) systems include MHC molecules, costimulatory molecules, and cytokines such as IL-2, IL-4, IL-6, GM-CSF. These are intended to induce effective systemic immune responses against tumor antigens which would not otherwise develop. Direct toxic approaches include the reintroduction of tumor suppressor genes or enzymes which convert non-toxic drugs to toxic ones, such as herpes thymidine kinase. As a means for gene delivery, retroviruses are the most common vehicle, although Adenovirus vectors and direct DNA delivery have specific advantages.

Rate of Clearance of Vibrio fetus var. venerealis in the Rabbit

The rate of clearance of Vibrio fetus var. venerealis was measured by using in vivo and in vitro methods. The rate of clearance from the circulating blood increased in immune rabbits and reached a plateau 4 days after immunization. Thereafter in vivo clearance did not increase further despite rising agglutinin titers. Vibriocidal activity of freshly drawn blood paralleled the rate of in vivo clearance although it was less effective at 4 days. Vibriocidal activity of immune serum was not demonstrated at the same intervals of time as the freshly drawn blood. Vibriocidal activity of immune sera plus complement was demonstrated after 1 hr of incubation at 37 C in a candle jar. An effective systemic immune response to V. fetus var. venerealis can be elicited in the rabbit. These results suggest that humoral antibodies play an important role in effecting acquired immunity against V. fetus var. venerealis.