1. Course faculty: Imon Rahman

2. Immunological Products Immunological products comprise a group of pharmaceutical preparations with diverse origins but with a common pharmacological purpose: the modification of the immune status of the recipient, either to provide immunity to infectious disease, or in the case of in vivo diagnostics, to provoke an indication of immune status. The immunological products that are currently available are of the following types: Vaccines Human immunoglobulins; Monoclonal antibodies

3. Live (attenuated) vaccines These are preparations of live bacteria, viruses or other agents which, when administered by an appropriate route, cause subclinical or mild infections. In the course of such an infection the components of the microorganisms in the vaccine evoke an immune response which provides protection against the more serious natural disease. Vaccinia was eventually used to eradicate smallpox. Its significance was that it could stimulate a high degree of immunity to smallpox while producing only a localized infection in the recipient. Treatment of a virulent strain of Salmonella typhi with nitrosoguanidine, which produced multiple mutations, gave rise to the live attenuated typhoid vaccine strain Ty21a. More recently developed attenuated strains of S. typhi and Vibrio cholerae have been selected by directed mutagenesis processes which can produce defined mutations in specific genes.

4. Killed vaccines. Killed vaccines are suspensions of bacteria, viruses or other pathogenic agents that have been killed by heat or by disinfectants such as phenol, ethanol or formaldehyde. Killed microorganisms obviously cannot replicate and cause an infection and so it is necessary for each dose of a killed vaccine to contain sufficient antigenic material to stimulate a protective immune response. Killed vaccines therefore usually have to be relatively concentrated suspensions. Even so, such preparations are often rather poorly protective, possibly because of partial destruction of protective antigens during the killing process or inadequate expression of these during in vitro culture. Such a course of vaccination takes advantage of the enhanced ‘secondary’ response that occurs when a vaccine is administered to an individual person whose immune system has been sensitized by a previous dose of the same vaccine. The best known killed vaccines are whooping cough (pertussis), typhoid, cholera, plague, inactivated polio vaccine (Salk type) and rabies vaccine.

5. Toxoid vaccines Toxoid vaccines are preparations derived from the toxins that are secreted by certain species of bacteria. In the manufacture of such vaccines, the toxin is separated from the bacteria and treated chemically to eliminate toxicity without eliminating immunogenicity, a process termed ‘toxoiding’. A variety of reagents have been used for toxoiding, but by far the most widely employed and generally successful has been formaldehyde. Toxoid vaccines are very effective in the prevention of those diseases such as diphtheria, tetanus, botulism and clostridial infections of farm animals, in which the infecting bacteria produce disease through the toxic effects of secreted proteins which enzymically modify essential cellular components.

6. Bacterial cell component vaccines Rather than use whole cells, which may contain undesirable and potentially reactogenic components such as lipopolysaccharide endotoxins, a more precise strategy is to prepare vaccines from purified protective components. These are of two main types, proteins and capsular polysaccharides. Often more than one component may be needed to ensure protection against the full range of prevalent serotypes. The potential advantage of such vaccines is that they evoke an immune response only to the component, or components, in the vaccine and thus induce a response that is more specific and effective. e.g Haemophilus influenzae type b vaccine; the Neisseria meningitidis vaccines; the 23-valent pneumococcal polysaccharide vaccine.

7. Conjugate vaccines The performance of certain types of antigen that give weak or inappropriate immune responses can often be improved by chemically conjugating them to more immunogenic carriers. Polysaccharide–protein, peptide–protein, protein– protein, lipid–protein and alkaloid–protein conjugate vaccines may be prepared in this way. These have a wide range of applications, including prevention of infection, tumor therapy, fertility control and treatment of addictions. This approach has been very successful against infections caused by bacteria that produce polysaccharide capsules.

8. Viral subunit vaccines Three viral subunit vaccines are widely available, two influenza vaccines and a hepatitis B vaccine. The influenza vaccines are prepared by treating intact influenza virus particles (from embryonated hens’ eggs infected with influenza virus) with a surface-active agent such as a nonionic detergent. This disrupts the virus particles, releasing the virus subunits. The two that are required in the vaccine, haemagglutinin and neuraminidase, can be recovered and concentrated by centrifugation methods. The hepatitis B vaccine was, at one time, prepared from hepatitis B surface antigen (HbsAg) obtained from the blood of carriers of hepatitis B virus.

9. Enzymatic Destruction or Inactivation of the Drug Destruction or inactivation by enzymes mainly affects antibiotics that are natural products, such as the penicillins and cephalosporins. Totally synthetic chemical groups of antibiotics such as the fluoroquinolones are less likely to be affected in this manner, although they can be neutralized in other ways. This may simply reflect the fact that the microbes have had fewer years to adapt to these unfamiliar chemical structures. The penicillin/cephalosporin antibiotics share a structure, the β- lactam ring, which is the target for β-lactamase enzymes that selectively hydrolyze it. Nearly 200 variations of these enzymes are now known, each effective against minor variations in the β- Iactam ring structure. When this problem first appeared, the basic penicillin molecule was modified. The first of these penicillinase-resistant drugs was methicillin, but resistance to methicillin soon appeared.

10. Prevention of Penetration to the Target Site within the Microbe Gram-negative bacteria are relatively more resistant to antibiotics because of the nature of their cell wall, which restricts absorption of many molecules through openings called porins. Some bacterial mutants modify the porin opening so that antibiotics are unable to enter the periplasmic space. Perhaps even more important, when present in the periplasmic space, the antibiotic remains outside the cell, where the enzyme, which is too large to enter even through an unmodified porin, can reach and inactivate it.

11. Alteration of the Drug's Target Site The synthesis of proteins involves the movement of a ribosome along a strand of messenger RNA. Several antibiotics, especially those of the aminoglycoside, tetracycline groups, inhibit protein synthesis at this site. Minor modifications at this site can neutralize the effects of antibiotics without significantly affecting cellular function. Interestingly, the main mechanism by which MRSA gained resistance to methicillin was not by a new inactivating enzyme, but by modifying the penicillin- binding protein (PBP) on the cell's membrane.

12. Rapid Efflux (Ejection) of the Antibiotic Certain proteins in the plasma membranes of gram- negative bacteria act as pumps that expel antibiotics, preventing them from reaching an effective concentration. This mechanism was originally observed with tetracycline antibiotics, but it confers resistance to practically all major classes of antibiotics. Bacteria normally have many such efflux pumps to eliminate toxic substances. Variations on these above mechanisms also occur. For example, a microbe could become resistant to trimethoprim by synthesizing very large amounts of the enzyme against which the drug is targeted. Conversely, polyene antibiotics can become less effective when resistant organisms produce smaller amounts of the sterols against which the drug is effective.