|
Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 91, Num. 6, 1996
|
Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(6),
Nov./Dec. 1996,
RESEARCH NOTE
Phase I and II Open Clinical Trials of a Vaccine Against
Leishmania chagasi Infections in Dogs
Wilson Mayrink, Odair Genaro/+, Joao Carlos Franca Silva,
Roberto Teodoro da Costa, Wagner Luis Tafuri*, Vicente Paulo C
Peixoto Toledo**, Alexandre Rotondo da Silva***, Alexandre
Barbosa Reis***/++, Paul Williams, Carlos Alberto da
Costa**
Departamento de Parasitologia *Departamento de Patologia
Geral, Instituto de Ciencias Biologicas **Departamento de
Analises Clinicas e Toxologicas, Faculdade de Farmacia,
Universidade Federal de Minas Gerais, Av. Antonio Carlos 6627,
Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brasil
***Departamento de Ciencias Biologicas, Universidade Federal
de Ouro Preto, Ouro Preto, MG, Brasil
This work received financial support from Fundacao Banco do
Brasil, FAPEMIG and BIOBRAS.
+Corresponding author. Fax: +55-31-441.6909
++Fellowship of CNPq
Received 26 March 1996, Accepted 16 August 1996
Key words: canine visceral leishmaniasis - Leishmania
chagasi - vaccine - dogs
Code Number: OC96124
Sizes of Files:
Text: 11.9K
Graphics: No associated graphics files
Visceral leishmaniasis occurs in tropical and subtropical
parts of the world and is most commonly found in rural areas.
In the Americas, more than 90% of the cases have been
recorded in Brazil. The disease can be controlled by
treatment of all human cases, elimination of infected dogs and
application of insecticide to the walls of dwellings and
peridomestic buildings (PA Magalhaes et al. 1980 Rev Inst
Med Trop Sao Paulo 22: 197-202). After applying these
measures, constant vigilance must be exercised. Control
measures must be applied again as soon as there is evidence of
the reactivation of the transmission cycle.
As alternative control measures some authors have emphasized
the importance of immunopro-phylaxis for canine visceral
leishmaniasis (CVL) (MCA Marzochi et al. 1985 Mem Inst
Oswaldo Cruz 80: 349-357, L Monjour et al. 1985 CR
Acad Sc Paris 301: 803-806). Observations in Europe,
however, have produced contradictory results. The vaccine
used by Monjour (loc. cit.) and D Frommel et al.
(1988 Infect Immun 56: 843) protected mice against
Leishmania mexicana and L. major, and was found
to stimulate the production of neutralizing antibodies when
given to dogs (S Dunan et al. 1989 Parasite Immunol 11:
397-402). A similar vaccine incorporating L. infantum
(semi-purified and lyophilized) was used in a pilot study of
domestic dogs in an endemic area of CVL (BV Ogunkolade 1988
Vet Parasitol 28: 33-41). Surprisingly, vaccinated
dogs were found to be more susceptible to infection than the
controls. In Brazil, W Mayrink et al. (1990 Rev Inst Med
Trop Sao Paulo 32: 67-69) found that dogs can be
partially protected against cutaneous leishmaniasis by a
vaccine prepared from a single stock of L.
braziliensis.
Presently, this line of study has been developed to explore
protection of dogs against infection with L. chagasi.
In order to evaluate the safety (phase I) and
immunogenicity/efficacy (phase II) of this vaccine against
CVL, we carried out experiments in dogs with experimental
challenge of promastigotes of L. chagasi (strain
MHOM/BR/72/BH46) after immunization.
Thirty one 4 month-old laboratory-reared mongrel dogs of both
sexes were immunized against parvovirosis, leptospirosis,
distemper, parainfluenza and hepatitis and treated with
mebendazol for intestinal helminthic infections.
The Leishmania vaccine was composed of merthyolated
sound-disrupted promastigotes of L. braziliensis,
strain MCAN/BR/72/C348 (Mayrink loc. cit.). The
promastigotes were cultured in NNN/LIT media (EP Camargo 1964
Rev Inst Med Trop Sao Paulo 6: 43-100). The flagelates
were submitted to ultra-sound during 1 min at 40 watts, in an
ice bath. The process was repeated three times, at 1 min
intervals. Total nitrogen content was then determined and the
extracts were diluted in saline mixed with thimerozal
(1:10,000), adjusting the final concentration to 240 ug of
total N/ml. Bacillus Calmete Guerin (BCG - Fundacao Ataulfo
de Paiva, Rio de Janeiro) was added as an adjuvant.
The phase I trial was carried out on 12 non-immune dogs, and
the aim was to evaluate the kinetics of the inflammatory skin
reaction to the vaccine and BCG and to determine localized and
systemic side effects. Four groups composed of three dogs each
were used. In Group I dogs received an injection of vaccine
containing 600 ug protein mixed with 400 ug of BCG. Animals
in groups II, III and IV received BCG (400 ug), vaccine or
PBS, respectively. All dogs received intradermal injections
(300 ul each) in six distinct sites on the back. Skin
biopsies were taken from each site of the inocula after 7, 14,
21, 28, 35 and 42 days, fixed in buffered (pH 7.2) formol
saline, sectioned (5 um-thick), and stained with haematoxylin
and eosin and/or Gomori. The dogs were clinically examined
during the experiment and rectal temperature was taken on the
days mentioned above.
Histologically, all animals from Group I that received BCG
combined with vaccine showed an intense, chronic inflammatory
reaction that increased progressively in the outer and deeper
layers of the dermis. On day 21, the epidermis was replaced
by ulcer and the dermis contained an intense exudate of
neutrophils, macrophages, lymphocytes and plasma cells, mixed
with necrotic tissue on the bed of the ulcer. On days 28 and
35, the inflammatory reaction became chronic, productive, and
granulomatous. After 35 days, there was a tendency for
fibrosis, with fibroblastic proliferation and local deposition
of collagen. Dogs receiving only BCG (Group II) presented a
chronic and diffuse inflammatory reaction that was
qualitatively similar to the vaccine plus BCG group, but
quantitatively less intense, mainly at days 21 and 28. Animals
from Group III, receiving only vaccine, displayed a moderate
inflammatory reaction observed only on day 21, characterized
by an exudate composed by mononuclear cells, plasma cells and
a few neutrophils. In the animals from Group IV that received
only PBS no inflammatory reaction was observed.
This study showed an absence of adverse reactions in dogs
inoculated with the vaccine and/or BCG. The local reaction
with granuloma and ulcer formation was circumscribed at the
site of injection. No fever or satellite adenitis were
observed.
Phase II was carried out on 19 dogs randomly divided in two
groups: vaccinated group (10 dogs vaccinated with vaccine plus
BCG) and control group (9 unvaccinated controls). Three doses
of vaccine (600 ug protein/dose) mixed with BCG (400 ug/dose)
were given intradermally at 21-day intervals. Sixty days after
the third dose, all dogs received an intravenous challenge
with 2.3x106 infective promastigotes of the parasites. All
dogs were followed up at two month intervals with aspirative
biopsies of bone marrow (Giemsa-stained smears and by
culture in NNN/LIT medium) together with blood collections for
anti-Leishmania immunofluorescence antibody test (IFAT)
to detect IgG. Cell-mediated immune response was assessed by
lymphocyte proliferation assay, employing peripheral
mononuclear blood cells (E Nascimento et al. 1990 Infect
Immun 58: 2198-2203).
Table shows the final results after 26-months of follow up
(necropsy was performed in all dogs to detect parasites). At
this time, 1/10 dogs in the vaccinated group showed patent
L. chagasi infection whereas in the unvaccinated
control dogs all animals developed infection. On the
subsequent days after the immunization, the vaccinated dogs
did not produce specific anti-Leishmania antibodies
detectable by IFAT. These were detected in some animals at
different levels three months after the inocula of the
promastigotes, indicating infection by Leishmania and
not antibody production due to immunization.
Nine of ten vaccinated dogs showed positive stimulation index
responses 15 days after the third immunization dose and during
the follow-up, but the control dogs were unresponsive. A
proliferation response was considered positive when calculated
lymphocyte proliferation rate in face of Leishmania
antigens was +/- 2.5 (SC Mendonca et al. 1986 Clin Exp
Immunol 64: 269-276).
These results indicate that the combined vaccine/BCG tested
is safe and did not give rise to adverse side effects in
inoculated dogs. The immunogenic effect of the combined
vaccine/BCG was demonstrated by the induction of cellular
immunity and the partial protection of dogs when challenged.
Use of a strain of L. braziliensis combined with BCG as
a vaccine against L. chagasi infection could be
effective against the disease in dogs, since Ogunkolade
(loc. cit.) has already shown that a vaccine prepared
with L. infantum increases the susceptibility of dogs
to the parasite. It is possible that antigens of L.
chagasi have an immunossupressive effect. The use of the
BCG as adjuvant together with the first generation vaccines
composed of killed parasite for clinical trial has been
recommended by the Leishmaniasis Vaccine Steering Committee of
the WHO/TDR Programme.
In view of these results, we have begun a third phase
consisting of a randomized, double blind clinical trial of the
vaccine combined with BCG. This is being carried out in Montes
Claros, in the north of the State of Minas Gerais, Brazil,
where the disease is endemic and 34 autochthonous human cases
were diagnosed in 1994.
TABLE: Parasitological and immunological observations on 19
dogs challenged with promastigotes of Leishmania
chagasi after immunization with a vaccine against visceral
leishmaniasis
Group Dog Parasite Stimulation Reciprocal Conclusion
isolation^a index of of IFAT (infection)
lymphocyte titres^c
proliferation
assay^b
------------------------------------------------------------------
1 Negative 14.3 Negative No
2 Negative 13.0 Negative No
3 Negative 5.6 Negative No
4 Negative 3.3 Negative No
5 Negative 5.6 Negative No
Vaccinated 6 Negative 3.3 Negative No
7 Negative 6.6 Negative No
8 Positive 1.9 1:160 Yes
9 Negative 3.9 Negative No
10 Negative 4.7 Negative No
11 Negative 1.0 1:360 Yes
12 Negative 1.7 1:640 Yes
13 Negative 2.1 1:360 Yes
14 Positive 2.1 1:1280 Yes
Control 15 Positive 1.7 1:160 Yes
16 Positive 1.3 1:2560 Yes
17 Negative 0.8 1:640 Yes
18 Positive 0.7 1:1280 Yes
19 Positive 0.8 1:1280 Yes
^a: final results obtained on the day of the animals'
necropsies; ^b: results obtained after the third dose of the
vaccine; ^c: IFAT= immunofluorescent antibody test.
Copyright 1996 Fundacao Oswaldo Cruz
|