Mycobacterium bovis BCG priming induces a strong potentiation of the antibody response induced by recombinant BCG expressing a foreign antigen

Robust immunity to an auxotrophic Mycobacterium bovis BCG-VLP prime-boost HIV vaccine candidate in a nonhuman primate model

We previously reported that a recombinant pantothenate auxotroph of Mycobacterium bovis BCG expressing human immunodeficiency virus type 1 (HIV-1) subtype C Gag (rBCGpan-Gag) efficiently primes the mouse immune system for a boost with a recombinant modified vaccinia virus Ankara (rMVA) vaccine. In this study, we further evaluated the immunogenicity of rBCGpan-Gag in a nonhuman primate model. Two groups of chacma baboons were primed or mock primed twice with either rBCGpan-Gag or a control BCG. Both groups were boosted with HIV-1 Pr55(gag) virus-like particles (Gag VLPs). The magnitude and breadth of HIV-specific cellular responses were measured using a gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISPOT) assay, and the cytokine profiles and memory phenotypes of T cells were evaluated by polychromatic flow cytometry. Gag-specific responses were detected in all animals after the second inoculation with rBCGpan-Gag. Boosting with Gag VLPs significantly increased the magnitude and breadth of the responses in the baboons that were primed with rBCGpan-Gag. These responses targeted an average of 12 Gag peptides per animal, compared to an average of 3 peptides per animal for the mock-primed controls. Robust responses of Gag-specific polyfunctional T cells capable of simultaneously producing IFN-γ, tumor necrosis alpha (TNF-α), and interleukin-2 (IL-2) were detected in the rBCGpan-Gag-primed animals. Gag-specific memory T cells were skewed toward a central memory phenotype in both CD4(+) and CD8(+) T cell populations. These data show that the rBCGpan-Gag prime and Gag VLP boost vaccine regimen is highly immunogenic, inducing a broad and polyfunctional central memory T cell response. This report further indicates the feasibility of developing a BCG-based HIV vaccine that is safe for childhood HIV immunization.

A prime-boost immunisation regimen using recombinant BCG and Pr55(gag) virus-like particle vaccines based on HIV type 1 subtype C successfully elicits Gag-specific responses in baboons

Mycobacterium bovis BCG is considered an attractive live bacterial vaccine vector. In this study, we investigated the immune response of baboons to a primary vaccination with recombinant BCG (rBCG) constructs expressing the gag gene from a South African HIV-1 subtype C isolate, and a boost with HIV-1 subtype C Pr55(gag) virus-like particles (Gag VLPs). Using an interferon enzyme-linked immunospot assay, we show that although these rBCG induced only a weak or an undetectable HIV-1 Gag-specific response on their own, they efficiently primed for a Gag VLP boost, which strengthened and broadened the immune responses. These responses were predominantly CD8+ T cell-mediated and recognised similar epitopes as those targeted by humans with early HIV-1 subtype C infection. In addition, a Gag-specific humoral response was elicited. These data support the development of HIV-1 vaccines based on rBCG and Pr55(gag) VLPs.

Rabbits immunised with recombinant BCG expressing the cottontail rabbit papillomavirus (CRPV) L2E7E2 genes induces regression of established papillomas

We previously demonstrated in a cottontail rabbit papillomavirus (CRPV) challenge model that recombinant Bacille Calmette-Guerin (rBCG) could potentially be used as a prophylactic vaccine vehicle to deliver papillomavirus proteins. In this study we investigated whether regression of CRPV-induced papillomas could be achieved following immunisation of out-bred New Zealand White rabbits with rBCG expressing CRPVL2, CRPVE2, CRPVE7 or CRPVL2E7E2 proteins. Rabbits immunised with rBCG/CRPVL2E7E2 had papillomas that were largely suppressed and were significantly smaller compared to the rBCG negative control group (P</=0.01). In addition, four of the six rabbits immunised with rBCG/CRPVL2E7E2 had papillomas that completely regressed 1.5 weeks post third immunisation. Rabbits immunised with rBCG/CRPVL2, rBCG/CRPVE7, or rBCG/CRPVE2 had papillomas that were significantly smaller than the negative control rabbits (P</=0.05). The findings in this study suggest that BCG could probably be used as a vaccine delivery vehicle for human papillomavirus proteins as a possible therapeutic vaccine.

Immune response induced by recombinant Mycobacterium bovis BCG expressing ROP2 gene of Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite, capable of infecting a variety of mammals and birds. Development of vaccine against T. gondii would be of great medical and veterinary value. In this study, the DNA sequence encoding ROP2 from T. gondii was cloned into the muticopy mycobacterial expression vector, pMV262, under the control of the Bacillus Calmette-Guerin (BCG) hsp60 promoter, and electroporated into BCG. Following selection of kanamycin, the recombinant BCG/pMV262-ROP2 was constructed and the expression of ROP2 was confirmed by Western blotting. The BALB/c mice inoculated with the BCG/pMV262-ROP2 developed specific immune responses against ROP2 protein, and there was an obvious delay in the mortality curve than the control (P<0.05). These results indicated that M. bovis BCG is an adequate vector to express and present antigens of T. gondii, and it may be used to further study the induction of protective immunity in other animals.

Progress towards an HIV vaccine based on recombinant bacillus Calmette-Guérin: failures and challenges

The need for an affordable, safe and effective HIV vaccine has never been greater. As the immunogenicity of all the vaccine vectors being evaluated currently in human populations is limited, novel vaccine strategies are needed to stimulate the innate immune system, to generate high levels of neutralizing antibodies and to induce strong cell-mediated and mucosal immunity. There is strong evidence for a role for cytotoxic T lymphocytes in the containment of HIV replication. Several vaccine approaches have been tested to elicit anti-HIV cytotoxic T-lymphocyte responses. One promising approach is Bacillus Calmette-Guérin (BCG) as a bacterial live recombinant vaccine vehicle. BCG has a long record of safety in humans and is able to induce long-lasting immunity. In this review, we describe the limitations and challenges of developing a recombinant BCG-based HIV vaccine. We also emphasize possible approaches for overcoming the plasmid instability in vivo and the low levels of gene expression and immunogenicity induction. Today, projects all over the world are focused on the development of an AIDS vaccine. Overcoming the remaining scientific, logistical and financial hurdles to the development of an effective HIV vaccine will require real imagination and firm commitment from all stakeholders.

A role for dendritic cells in the dissemination of mycobacterial infection

The ability of mycobacteria to disseminate from the initial site of infection has an important role in immune priming and in the seeding of disease in multiple organs. To study this phenomenon, we used flow cytometry to analyse the distribution of green fluorescent protein-labelled BCG amongst different populations of antigen-presenting cells in the lungs of mice following intranasal infection, and monitored appearance of live bacteria in the draining mediastinal lymph nodes. BCG predominantly infected alveolar macrophages (CD11c(+)/CD11b(-)) and dendritic cells (CD11c(+)/CD11b(+)) in the lungs. The bacteria that disseminated to the lymph node were found in dendritic cells. The results are consistent with a model in which mycobacterial dissemination from the lung is initiated by the migration of infected dendritic cells to the draining lymph nodes.

Generation of CD8+ T-cell responses by a recombinant nonpathogenic Mycobacterium smegmatis vaccine vector expressing human immunodeficiency virus type 1 Env

Because the vaccine vectors currently being evaluated in human populations all have significant limitations in their immunogenicity, novel vaccine strategies are needed for the elicitation of cell-mediated immunity. The nonpathogenic, rapidly growing mycobacterium Mycobacterium smegmatis was engineered as a vector expressing full-length human immunodeficiency virus type 1 (HIV-1) HXBc2 envelope protein. Immunization of mice with recombinant M. smegmatis led to the expansion of major histocompatibility complex class I-restricted HIV-1 epitope-specific CD8(+) T cells that were cytolytic and secreted gamma interferon. Effector and memory T lymphocytes were elicited, and repeated immunization generated a stable central memory pool of virus-specific cells. Importantly, preexisting immunity to Mycobacterium bovis BCG had only a marginal effect on the immunogenicity of recombinant M. smegmatis. This mycobacterium may therefore be a useful vaccine vector.

Immunisation with recombinant BCG expressing the cottontail rabbit papillomavirus (CRPV) L1 gene provides protection from CRPV challenge

Recombinant Bacille Calmette-Guerin (rBCG) could potentially be the vaccine vehicle of choice to deliver foreign antigens from multiple pathogens. In this study we have used the cottontail rabbit papillomavirus (CRPV) rabbit model to provide a "proof of concept" that immunisation with rBCG expressing the CRPV major capsid protein, L1 (rBCG/CRPVL1), will protect outbred New Zealand White rabbits against CRPV challenge. Rabbits immunised with rBCG/CRPVL1 (10(7) cfu/ml) were protected 5 weeks post-CRPV challenge. Rabbits immunised with rBCG/CRPVL1 (10(5) cfu/ml) had papillomas, which were smaller and took longer to appear than the control rabbits. None of the negative control rabbits vaccinated with rBCG expressing an irrelevant gene or PBS were protected from CRPV challenge. Sera from rabbits immunised with rBCG/CRPVL1 (10(7) cfu/ml) were able to neutralise 54.5% of CRPV at serum dilutions of 1:200. These results provide evidence that BCG could potentially be used as a vaccine delivery vehicle for human papillomavirus proteins as a possible prophylactic vaccine.

Factors influencing the immune response to foreign antigen expressed in recombinant BCG vaccines

A wide range of recombinant BCG vaccine candidates containing foreign viral, bacterial, parasite or immunomodulatory genetic material have been developed and evaluated, primarily in animal models, for immune response to the foreign antigen. This review considers some of the factors that may influence the immunogenicity of these vaccines. The influence of levels and timing of expression of the foreign antigen and the use of targeting sequences are considered in the first section. Genetic and functional stability of rBCG is reviewed in the second section. In the last section, the influence of dose and route of immunization, strain of BCG and the animal model used are discussed.

Novel vaccination strategies based on recombinant Mycobacterium bovis BCG

In this manuscript, we will review the utilization of Mycobacterium bovis Bacille Calmette-Guerin (BCG) as a vaccine against tuberculosis (TB) and as a carrier system for heterologous antigens. BCG is one of the most widely used vaccines. Novel techniques in genome manipulation allow the construction of virulence-attenuated recombinant (r)-BCG strains that can be employed as homologous vaccines, or as heterologous antigen delivery systems, for priming pathogen-specific immunity against infectious diseases, including TB. Several approaches are available for heterologous antigen expression and compartmentalization in BCG and recent findings show the potential to modulate and direct the immune responses induced by r-BCG strains as desired. Recent achievements in complete genome analysis of various target pathogens, combined with a better understanding of protective pathogen-specific immune responses, form the basis for the rational design of a new generation of recombinant mycobacterial vaccines against a multitude of infectious diseases.

Vaccination against ovine footrot using a live bacterial vector to deliver basic protease antigen

A strain of Corynebacterium pseudotuberculosis, designated Toxminus, that has been rationally attenuated by deletion of the phospholipase D gene, is being developed as a live vaccine vector for the delivery of veterinary vaccine antigens. In the present study a recombinant form of the basic protease gene of the ovine footrot causative bacterium, Dichelobacter nodosus, was introduced into the vector strain using the high copy number plasmid pEP2. This strain secreted the basic protease protein. Vaccination trials in sheep with the recombinant strain demonstrated that, although an IgG immune response was elicited, the animals were not protected from footrot following artificial challenge under pen conditions. Although the sheep were not protected there was evidence that the progression of the disease was slowed.

A single strain of Mycobacterium bovis bacillus Calmette-Guérin (BCG) grown in two different media evokes distinct humoral immune responses in mice

Two attenuated bacillus Calmette-Guérin (BCG) preparations derived from the same Moreau strain, Copenhagen but grown in Sauton medium containing starch and bacto-peptone (onco BCG, O-BCG), or asparagine (intradermal BCG, ID-BCG), exhibited indistinguishable DNA sequences and bacterial morphology. The number of viable bacilli recovered from spleen, liver and lungs was approximately the same in mice inoculated with the vaccines and was similarly reduced (over 90%) in mice previously immunized with either BCG vaccine. The humoral immune response evoked by the vaccines was, however, distinct. Spleen cell proliferation accompanying the growth of bacilli in tissue was significantly higher in mice inoculated with O-BCG. These cells proliferated in vitro upon challenge with the corresponding BCG extract. Previous cell treatment with mAb anti-CD4 T cells abolished this effect. Anti-BCG antibodies, as assayed either in serum by ELISA or by determining the number of antibody-producing spleen cells by the spot-ELISA method, were significantly higher in mice inoculated with ID-BCG. Anti-BCG antibodies were detected in all immunoglobulin classes, but they were more prevalent in IgG with the following distribution among its isotypes: IgG1>(IgG2a = IgG2b)>IgG3. When some well-characterized Mycobacterium tuberculosis antigens were used as substitutes for BCG extracts in ELISA, although antibodies against the 65-kDa and 96-kDa proteins were detected significantly, antibodies against the 71-kDa, 38-kDa proteins and lipoarabinomannan were only barely detected or even absent. These results indicate that BCG bacilli cultured in Sauton-asparagine medium permitted the multiplication of bacilli, tending to induce a stronger humoral immune response as compared with bacilli grown in Sauton-starch/bacto-peptone-enriched medium.

Recombinant bacillus Calmette-Guérin as a potential vector for preventive HIV type 1 vaccines

In August 1997, the World Health Organization (WHO) and the Joint United Nations Programme on HIV/AIDS (UNAIDS) convened an expert working group to discuss current strategies for the development of HIV type 1 vaccines. Based on the recent findings of investigators from Japan's National Institute of Infectious Diseases (NIID) in Tokyo using recombinant bacillus Calmette-Guérin (rBCG) as a potential vectored vaccine for HIV, a recommendation was made that further work in this area is a priority. As a result, the working group reconvened in September 1998 to discuss the progress to date with this vaccine approach, as well as areas of related research to assess the feasibility of a BCG-vectored HIV vaccine. This report summarizes the discussions addressing the available scientific data on the potential use of rBCG as a vector for preventive HIV vaccines, the work necessary to move such candidate vaccines into Phase 1 clinical trials, and recommendations targeted at facilitating the long-term development of rBCG-vectored HIV vaccines.

Long-lasting protective immunity against rodent malaria parasite infection at the blood stage by recombinant BCG secreting merozoite surface protein-1

Previously, we constructed a recombinant live BCG (rBCG) secreting a 15 kDa C-terminal region of MSP-1 from Plasmodium yoelii (MSP-1(15)) and succeeded in the induction of more efficient protective immunity against parasite infection than observed with artificial adjuvants (Matsumoto S, Yukitake H, Kanbara H, Yamada T. Recombinant Mycobacterium bovis bacillus Calmette-Guerin secreting merozoite surface protein 1 (MSP-1) induces protection against rodent malaria parasite infection depending on MSP-1-stimulated interferon gamma and parasite-specific antibodies. J Exp Med 1998;188:845-54 [1]). In this study, we examined the endurance of the protective effects. The protective effect generated by rBCGMSP-1(15) was observed even 9 months after final immunization, whereas the effects of immunization by MSP-1(15) together with incomplete Freund adjuvant (IFA) were found to last only 4 months.

Safety and immunogenicity of recombinant Bacille Calmette-Guérin (rBCG) expressing Borrelia burgdorferi outer surface protein A (OspA) lipoprotein in adult volunteers: a candidate Lyme disease vaccine

This phase I clinical trial was designed to determine the feasibility of using rBCG as a live bacterial vaccine vector for the outer surface protein A (OspA) of Borrelia burgdorferi and as model for other vaccines based on a rBCG vector. To construct the vaccine, a signal peptide derived from a mycobacterial lipoprotein was used to direct the export, and membrane-associated surface expression, of OspA in a standard strain of BCG (Connaught). The rBCG OspA vaccine was safe and immunogenic in several animal species, and protective in a mouse model of Lyme borreliosis. An intradermal injection (0.1 ml) of rBCG OspA was administered to 24 healthy adult volunteers sequentially at one of four dose levels, ranging from 2.0 x 10(4) CFU to 2 x 10(7) CFU, using a dose-escalation design. All volunteers were initially PPD-skin test and OspA antibody negative, and they were monitored for 2 years after immunization. Three volunteers had mild flu-like reactions 1-2 days after vaccination. Local ulceration and drainage at the site of injection, which occurred in 50% and 83% of volunteers in the two highest dose groups, persisted for 1-70 days before the ulcers healed. Most of the drainage samples yielded rBCG colonies that contained the OspA plasmid. Thirteen of 24 vaccinees, principally in the two highest dose groups, converted their PPD skin tests from negative to positive. None of the 24 volunteers developed OspA antibody. In conclusion, the current rBCG vaccine construct, the first such construct tested in humans, had a safety profile comparable to that of licensed BCG, but it did not elicit primary humoral responses to the vectored antigen.

A cocktail of Mycobacterium bovis BCG recombinants expressing the SIV Nef, Env, and Gag antigens induces antibody and cytotoxic responses in mice vaccinated by different mucosal routes

Recombinant live Mycobacterium bovis BCG strains (rBCG) expressing different human immunodeficiency virus (HIV) or simian immunodeficiency (SIV) antigens could be good candidates for the development of vaccines against AIDS. To develop effective HIV/SIV vaccines, humoral and cellular immune responses directed against multiple antigens may be essential for the control of the infection. In this study we immunized BALB/c mice via different mucosal routes (oral, aerogenic, nasal, and rectal) with a mixture of three rBCG strains expressing, respectively, the entire SIVmac251 Nef protein, and large fragments of the Env and Gag proteins. All routes of immunization studied induced immunoglobulin A (IgA) antibodies against mycobacterial PPD, SIV Env, and SIV Gag antigens in feces and bronchial lavages as well as specific immunoglobulin G (IgG) in serum. Strong, specific cytotoxic responses of splenocytes against Nef, Env, and Gag was observed whatever the mucosal route of immunization. Therefore, mucosal vaccination with a cocktail of rBCG strains induces local, specific IgA, systemic IgG, and systemic CTLs against the three SIV antigens expressed. Rectal and oral routes seemed the most appropriate route of vaccination to be used to protect against SIV infection.

The genetic reconstruction of BCG as a new immunotherapeutic tool

The bacillus of Calmette and Guérin (BCG), long appreciated for its role as a live vaccine for the prevention of tuberculosis, is undergoing a rebirth as a recombinant delivery vehicle for foreign antigens and bioactive proteins. Recombinant BCG causes long-lived specific humoral and cellular immunity and may ultimately prove to be a powerful and cost-effective new weapon against both infectious pathogens and certain cancers.

Genetic control of antibody responses induced by recombinant Mycobacterium bovis BCG expressing a foreign antigen

Recombinant Mycobacterium bovis BCG expressing foreign antigens represents a promising candidate for the development of future vaccines and was shown in several experimental models to induce protective immunity against bacterial or parasitic infections. Innate resistance to BCG infection is under genetic control and could modify the immune responses induced against an antigen delivered by such engineered microorganisms. To investigate this question, we analyzed the immune responses of various inbred strains of mice to recombinant BCG expressing beta-galactosidase. These experiments demonstrated that BALB/c mice developed strong antibody responses against BCG expressing beta-galactosidase under the control of two different promoters. In contrast, C57BL/6, C3H, and CBA mice produced high anti-beta-galactosidase antibody titers only when immunized with recombinant BCG expressing beta-galactosidase under the control of the pblaF* promoter, which induced the production of high levels of this antigen. This difference in mouse responsiveness to recombinant BCG was not due to innate resistance to BCG infection, since similar immune responses were induced in Ity(r) and Ity(s) congenic strains of mice. In contrast, the analysis of anti-beta-galactosidase antibody responses of H-2 congenic mice in two different genetic backgrounds demonstrated that H-2 genes are involved in the immune responsiveness to beta-galactosidase delivered by recombinant BCG. Together, these results demonstrate that immune responses to an antigen delivered by recombinant BCG are under complex genetic influences which could play a crucial role in the efficiency of future recombinant BCG vaccines.

Oral immunization with recombinant Mycobacterium bovis BCG simian immunodeficiency virus nef induces local and systemic cytotoxic T-lymphocyte responses in mice

Recombinant live Mycobacterium bovis BCG vectors (rBCG) induce strong cellular and humoral immune responses against various antigens after either systemic or oral immunization of mice. Cytotoxic T-lymphocyte (CTL) responses may contribute to the control of human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) infections whose portal of entry is the gastrointestinal or genital mucosa. In this study, we immunized BALB/c mice with a recombinant BCG SIV nef and observed its behavior in oropharyngeal and target organ lymphoid tissues. The cellular immune responses, particularly the intestinal intraepithelial and systemic CTL responses, were investigated. The results showed that rBCG SIV nef translocated the oropharyngeal mucosa and intestinal epithelium. It diffused to and persisted in target lymphoid organs. Specific SIV Nef peptide proliferative responses and cytokine production were observed. Strong systemic and mucosal CTL responses were induced. In particular, we demonstrated direct specific anti-Nef CTL in intestinal intraepithelial CD8beta+ T cells. These findings provide evidence that orally administered rBCG SIV nef may contribute to local defenses against viral invasion. Therefore, rBCG SIV nef could be a candidate vaccine to protect against SIV infection and may be used to develop an oral rBCG HIV nef vaccine.

Expression of foreign gene in mycobacterium regulated by human Mycobacterium tuberculosis heat shock protein 70 promoter

The DNA fragments of 150bp length promoter of human Mycobacterium (M.) tuberculosis heat shock protein (hsp) 70 and 650bp length foreign gene, the Schistosoma japonicum glutathione S-transferase (Sj26GST) gene, were obtained by amplification with polymerase chain reaction. And the 150bp DNA sequence upstream initiation codon ATG of the human M. tuberculosis hsp 70 promoter that contains the sequence TTGAG and ATCATA which consensus with E. coli promoter's -35 and -10 region respectively, as well as ribosome binding site GGAGG at position -12--8 upstream the ATG were determined by SangerDideoxyribonucleotide-mediated chain-termination method. Then, the human M. tuberculosis hsp70 promoter and Sj26GST cDNA were cloned into E. coli-mycobacteria shuttle plasmid pBCG- 2000 to construct E. coli-Mycobacterium expression shuttle plasmid pBCG- Sj26 that can express Sj26GST gene. The M. smegmatis were electroporated and the positivecolonies were selected by kanamycin. The M. smegmatis containing the vector pBCG-Sj26 can be induced by heating and hydrogen peroxide (H2O2) to express GST. The molecular weight of the recombinant GST (rGST) was 26,000. The rGST contents that were about 10 percent of the total bacterial protein were analyzed by density scanning after running SDS-PAGE. This study would provide scientific evidences for application of hsp70 promoter in expressing foreign gene in mycobacterium and development of mycobacterium as multiple-valent vectoral vaccine.

Immunogenicity and protection studies with recombinant mycobacteria and vaccinia vectors coexpressing the 18-kilodalton protein of Mycobacterium leprae

The activation of antigen-specific T lymphocytes is essential for the control of leprosy infection in humans and experimental animals. T cells recognize a variety of protein antigens from Mycobacterium leprae, including the 18-kDa protein, which is limited in distribution among mycobacteria and which is absent from Mycobacterium tuberculosis and the vaccine strain, Mycobacterium bovis BCG. Adjuvant preparations of mycobacterial protein antigens have had limited protective efficacy for experimental infections in animals. Since recombinant vectors may elicit more effective T-cell responses than adjuvant preparations, recombinant vaccinia virus (VV18) and M. bovis BCG (BCG18) vectors expressing the 18-kDa protein of M. leprae were prepared. Both VV18 and BCG18 stimulated anti-18-kDa protein antibody and lymphocyte proliferative responses. Sequential immunization with VV18 followed by BCG18 induced higher levels of specific immunoglobulin G2a antibodies than immunoglobulin G1 antibodies, in contrast to immunization with VV18 or BCG18 alone. The protective efficacy of immunization with VV18 from a challenge with BCG18 was examined in two murine models of mycobacterial infection. After intravenous challenge, mice immunized with recombinant vaccinia virus exhibited lower initial levels of replication and earlier clearance of BCG18 from their spleens than mice immunized with vaccinia virus expressing an unrelated protein. After footpad infection in a dissemination model, there was earlier clearance of BCG18 from specifically immunized mice. However, immunization of mice with VV18 did not prevent a productive mycobacterial infection.

Comparison of immune responses of mice immunized with five different Mycobacterium bovis BCG vaccine strains

Among the various parameters which may contribute to Mycobacterium bovis BCG vaccination efficiency, the choice of the vaccine strain may play an important role. In the present study, we therefore compared the immunogenicity of five different BCG strains that are commonly used for BCG vaccine production (Glaxo 1077, Japanese 172, Pasteur 1173P2, Prague, and Russian strains). The comparison of the growth capacity of these BCG strains in BALB/c and C3H mice demonstrated that a great difference exists between the capacity of various BCG strains to multiply and persist in target organs. A much lower recovery of BCG could be shown in mice immunized with Prague and Japanese BCG strains. T-cell responses of BCG-immunized mice were also examined by analyzing T-cell proliferative responses, cytokine production, delayed-type hypersensitivity responses, and cytotoxic activity. All these assays demonstrated that BCG immunization induced strong CD4+ T-cell responses, mostly of the Th1 type, as demonstrated by interleukin-2 and gamma interferon production. These studies also demonstrated that there are differences between BCG strains in stimulating these T-cell responses. A lack of induction of cytotoxic activity was observed following immunization with the Japanese strain. Lower anti-purified protein derivative antibody responses were also observed after intravenous or oral immunization with this BCG strain. Finally, the protective activity of these BCG strains was tested by measuring the capacity of immunized mice to eliminate recombinant Pasteur and Japanese BCG strains which expressed beta-galactosidase. The results of these experiments clearly demonstrated that the Prague and Japanese strains were unable to protect mice against a second mycobacterial challenge whereas mice immunized with the Glaxo, Pasteur, or Russian strain eliminated the recombinant BCG very efficiently. Altogether, the results of the present study strongly support the view that there are considerable differences in the immunogenicity of various BCG vaccine strains and that these differences may play a major role in BCG vaccination efficiency.