Drug – bio-affecting and body treating compositions – Antigen – epitope – or other immunospecific immunoeffector – Recombinant virus encoding one or more heterologous proteins...
Reexamination Certificate
2000-07-12
2004-03-02
Housel, James (Department: 1648)
Drug, bio-affecting and body treating compositions
Antigen, epitope, or other immunospecific immunoeffector
Recombinant virus encoding one or more heterologous proteins...
C424S202100, C424S205100, C424S211100, C435S069100
Reexamination Certificate
active
06699476
ABSTRACT:
BACKGROUND OF THE INVENTION
Human respiratory syncytial virus (HRSV) is the leading viral cause of serious pediatric respiratory tract disease worldwide (Collins, et al.,
Fields Virology
2:1313-1352, 1996; incorporated herein by reference). RSV outranks all other microbial pathogens as a cause of pneumonia and bronchiolitis in infants under one year of age. Virtually all children are infected by two years of age, and reinfection occurs with appreciable frequency in older children and young adults (Chanock et al., in
Viral Infections of Humans
, 3rd ed., A. S. Evans, ed., Plenum Press, N.Y., 1989; incorporated herein by reference). RSV is responsible for more than one in five pediatric hospital admissions due to respiratory tract disease, and in the United States alone causes nearly 100,000 hospitalizations and 4,500 deaths yearly. (Heilman,
J. Infect. Dis
. 161:402-6, 1990; incorporated herein by reference). In addition, there is evidence that serious respiratory tract infection early in life can initiate or exacerbate asthma (Sigurs, et al.,
Pediatrics
95:500-505, 1995; incorporated herein by reference).
While RSV usually is thought of in the context of the pediatric population, it also is recognized as an important agent of serious disease in the elderly (Falsey et al.,
J. Infect. Dis
. 172:389-394, 1995; incorporated herein by reference). RSV also causes life-threatening disease in certain immunocompromised individuals, such as bone marrow transplant recipients (Fouillard, et al.,
Bone Marrow Transplant
9:97-100, 1992; incorporated herein by reference).
For treatment of RSV, one chemotherapeutic agent, ribavirin, is available. However, its efficacy and use are controversial. There are also licensed products for RSV intervention which are composed of pooled donor IgG (Groothuis et al.,
N. Engl. J. Med
. 329:1524-1530, 1993; incorporated herein by reference) or a humanized RSV-specific monoclonal antibody. These are administered as passive immunoprophylaxis agents to high-risk individuals. While these products are useful, their high cost and other factors, such as lack of long-term effectiveness, make them inappropriate for widespread use. Other disadvantages include the possibility of transmitting blood-borne viruses and the difficulty and expense in preparation and storage. Moreover, the history of the control of infectious diseases, and especially diseases of viral origin, indicates the primary importance of vaccines.
Despite decades of investigation to develop effective vaccine agents against RSV, no safe and effective vaccine has yet been approved to prevent the severe morbidity and significant mortality associated with RSV infection. Failure to develop successful vaccines relates in part to the fact that small infants have diminished serum and secretory antibody responses to RSV antigens. Thus, these individuals suffer more severe infections from RSV, whereas cumulative immunity appears to protect older children and adults against more serious impacts of the virus.
The mechanisms of immunity in RSV infection have recently come into focus. Secretory antibodies appear to be most important in protecting the upper respiratory tract, whereas high levels of serum antibodies are thought to have a major role in resistance to RSV infection in the lower respiratory tract. RSV-specific cytotoxic T cells, another effector arm of induced immunity, are also important in resolving an RSV infection. However, while this latter effector can be augmented by prior immunization to yield increased resistance to virus challenge, the effect is short-lived. The F and G surface glycoproteins are the two major protective antigens of RSV, and are the only two RSV proteins which have been shown to induce RSV neutralizing antibodies and long term resistance to challenge (Collins et al.,
Fields Virology
, Fields et al. eds., 2:1313-1352, Lippincott-Raven, Philadelphia, 1996; Connors et al.,
J. Virol
. 65(3):1634-1637, 1991; incorporated herein by reference). The third RSV surface protein, SH, did not induce RSV-neutralizing antibodies or significant resistance to RSV challenge.
An obstacle to developing live RSV vaccines is the difficulty in achieving an appropriate balance between attenuation and immunogenicity. Other obstacles include the genetic instability of some attenuated viruses, the relatively poor growth of RSV in cell culture, and the instability of the virus particle. In addition the immunity which is induced by natural infection is not fully protective against subsequent infection. A number of factors probably contribute to this, including the relative inefficiency of the immune system in restricting virus infection on the luminal surface of the respiratory tract, the short-lived nature of local mucosal immunity, rapid and extensive virus replication, reduced immune responses in the young due to immunological immaturity, immunosuppression by transplacentally derived maternal serum antibodies, and certain features of the virus such as a high degree of glycosylation of the G protein. Also, as will be described below, RSV exists as two antigenic subgroups A and B, and immunity against one subgroup is of reduced effectiveness against the other.
Although RSV can reinfect multiple times during life, reinfections usually are reduced in severity due to protective immunity induced by prior infection, and thus immunoprophylaxis is feasible. A live-attenuated RSV vaccine would be administered intranasally to initiate a mild immunizing infection. This has the advantage of simplicity and safety compared to a parenteral route. It also provides direct stimulation of local respiratory tract immunity, which plays a major role in resistance to RSV. It also abrogates the immunosuppressive effects of RSV-specific maternally-derived serum antibodies, which typically are found in the very young. Also, while the parenteral administration of RSV antigens can sometimes be associated with immunopathologic complications (Murphy et al.,
Vaccine
8(5):497-502, 1990; incorporated herein by reference), this has never been observed with a live virus.
A formalin-inactivated virus vaccine was tested against RSV in the mid-1960s, but failed to protect against RSV infection or disease, and in fact exacerbated symptoms during subsequent infection by the virus. (Kim et al.,
Am. J. Epidemiol
., 89:422-434, 1969; Chin et al.,
Am J. Epidemiol
., 89:449-463, 1969; Kapikian et al.,
Am. J. Epidemiol
., 89:405-421, 1969; incorporated herein by reference).
More recently, vaccine development for RSV has focused on attenuated RSV mutants. Friedewald et al., (
J. Amer. Med. Assoc
. 204:690-694, 1968; incorporated herein by reference) reported a cold passaged mutant of RSV (cpRSV) which appeared to be sufficiently attenuated to be a candidate vaccine. This mutant exhibited a slightly increased efficiency of growth at 26° C. compared to its wild-type (wt) parental virus, but its replication was neither temperature sensitive nor significantly cold-adapted. The cold-passaged mutant, however, was attenuated for adults. Although satisfactorily attenuated and immunogenic for infants and children who had been previously infected with RSV (i.e., seropositive individuals), the cpRSV mutant retained a low level virulence for the upper respiratory tract of seronegative infants.
Similarly, Gharpure et al., (
J. Virol
. 3:414-421, 1969; incorporated herein by reference) reported the isolation of temperature sensitive RSV (tsRSV) mutants which also were promising vaccine candidates. One mutant, ts-1, was evaluated extensively in the laboratory and in volunteers. The mutant produced asymptomatic infection in adult volunteers and conferred resistance to challenge with wild-type virus 45 days after immunization. Again, while seropositive infants and children underwent asymptomatic infection, seronegative infants developed signs of rhinitis and other mild symptoms. Furthermore, instability of the ts phenotype was detected. Although virus exhibiting a partial or complete loss of temperature sensitivity represented a small proportion of vi
Bukreyev Alexander
Collins Peter L.
Murphy Brian P.
Whitehead Stephen S.
Chen Stacy B.
Graybeal Jackson Haley LLP
Housel James
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