MRC OX-22, a monoclonal antibody that labels a new subset of T lymphocytes and reacts with the high molecular weight form of the leukocyte-common antigen.

A mouse monoclonal antibody (MRC OX-22) is described that labels rat T cells which mediate graft-versus-host reactions and those responsible for the suppression of antibody synthesis in hosts undergoing these reactions. In contrast, most of the T cells that provide help for B cells are MRC OX-22 negative. These results, taken together with those published previously, demonstrate that the rat contains at least three phenotypically and functionally distinct subsets of T cells. The MRC OX-22 antibody also labels all B cells, 50% of bone marrow cells, but only 2% of thymocytes. Of these latter cells about half are found at the edge of the medulla and the remainder are randomly distributed throughout the cortex and medulla. These findings lend support to the view that mature thymocytes leave the thymus at the cortico-medullary junction, and also suggest that both cortex and medulla may be sites where thymocytes mature. Biochemical studies showed that the MRC OX-22 antibody reacts with the high molecular weight form of the leukocyte-common antigen (L-CA). Comparison with data on human L-CA suggests that the molecular and antigenic heterogeneity of this set of glycoproteins has been conserved between rat and man.

Naturally acquired antibodies to sporozoites do not prevent malaria: vaccine development implications.

The first human vaccines against the malaria parasite have been designed to elicit antibodies to the circumsporozoite protein of Plasmodium falciparum. However, it is not known whether any level of naturally acquired antibodies to the circumsporozoite protein can predict resistance to Plasmodium falciparum malaria. In this study, 83 adults in a malaria-endemic region of Kenya were tested for circumsporozoite antibodies and then treated for malaria. They were monitored for the development of new malaria infections for 98 days. Antibody levels, as determined by four assays in vitro, were indistinguishable between the 60 individuals who did and the 23 who did not develop parasitemia during follow-up, and there was no apparent relation between day of onset of parasitemia and level of antibodies to circumsporozoite protein. Unless immunization with sporozoite vaccines induces antibodies that are quantitatively or qualitatively superior to the circumsporozoite antibodies in these adults, it is unlikely that such antibodies will prevent infection in areas with as intense malaria transmission as western Kenya.

Molecular "Sameness" Is the Key Guiding Principle for Extrapolation to Multiple Indications.

Much has been made of biosimilars as a new regulatory concept, yet it is clear that misunderstandings are widespread, including the scientific justification for use in all indications of the reference product or "extrapolation." However, as this article shows, biosimilarity and extrapolation are not new concepts and most patients being treated with a branded biologic have already received a similar version of the original reference biologic based on changes in the manufacturing process.

Characterisation and sequence of a protective rhoptry antigen from Plasmodium falciparum.

We have recently demonstrated that a non-polymorphic rhoptry antigen, RAP-1 (rhoptry associated protein-1), which is recognised by human immune serum, can successfully protect Saimiri monkeys from a lethal infection of Plasmodium falciparum malaria. In this report we further characterise the antigen, which consists of four major proteins of 80, 65, 42 and 40 kDa and two minor proteins of 77 and 70 kDa, and present the antigen's gene sequence. Monoclonal antibody evidence, autocatalytic processing and immunological cross-reactivity suggest that all components of this antigen are derived from the same precursor protein. The antigen is lipophilic, and disulphide bonding plays an important role in its structure. We discuss the structure and function of RAP-1 in the light of its deduced amino acid sequence and consider the relationship of this antigen to other rhoptry antigens of similar subunit size and composition.

Innovation in biotechnology: current and future states.

Innovation is assumed to be a good thing in health care, just as it is elsewhere, and to be crucial to the availability of greater choices for consumers. But what is it? Very little definition is provided when the term is used. This report discusses the following aspects of biotech innovation: innovation in medicinal products, innovation in manufacturing processes, and innovation in regulatory science (both oversight and licensure).

Visualisation by low-angle shadowing of the leucocyte-common antigen. A major cell surface glycoprotein of lymphocytes.

The leucocyte-common antigen (L-CA) from rat thymocytes is a cell surface glycoprotein of 180 000 apparent mol. wt. with an 80-kd cytoplasmic domain. This paper reports the molecular dimensions of the molecule visualised by electron microscopy after low-angle shadowing. The L-CA monomer consists of a globular head region of approximately 12 nm diameter and a short tail approximately 18 nm long. In deoxycholate both monomers and multimers are seen with aggregation occurring at the head groups. When the detergent is removed, larger clusters are formed with tails extending from a central aggregate. A 100-kd tryptic fragment of L-CA that is known to include the extracellular parts of the molecule also exists in monomer and multimer forms and is seen to have a rod-like structure of length 28 nm without evidence of the head group. Altogether the data indicate that the rod-like structure is found outside the cell and that the extra sequence that forms the head is inside. The tryptic fragment is likely to be derived by cleavage after the transmembrane sequence.

Molecular and antigenic heterogeneity of the rat leukocyte-common antigen from thymocytes and T and B lymphocytes.

The molecular forms and antigenic heterogeneity of the leukocyte-common antigen (L-CA) of rat lymphocytes have been analyzed. Thymocytes show one main band at 180 kDa, T cells four bands at 180, 190, 200 and 220 kDa and B cells one broad band at about 240 kDa. T helper and T cytotoxic cell subsets show the same four bands with some differences in the proportion of each. Four mouse monoclonal antibodies (MRC OX-1, 28, 29 and 30) reacted with all molecular forms of L-CA and fell into two sets that were noncompetitive in binding to L-CA (MRC OX-1, 28, 29 vs. OX-30). The antigenic determinants seen by all these antibodies were lost when L-CA was reduced and alkylated. Three antibodies (MRC OX-22, 31 and 32) reacted selectively with B cells, T cytotoxic cells and about 2/3 of T helper cells. OX-22 and OX-31 competed for binding but were noncompetitive with OX-32. All these antibodies bound to a subfraction of the 190, 200 and 220-kDa forms of T cell L-CA but not at all to the 180-kDa form of T cells or thymocytes. One antibody bound to B cells only (MRC OX-33) and precipitated a subfraction of B cell L-CA. With all the antibodies that did not label thymocytes the antigenic determinants survived reduction and alkylation. Subsequent proteolysis with trypsin then destroyed all determinants except the one reacting with MRC OX-22 antibody. In this case tryptic peptides retained full antigenic activity which was, however, destroyed by further proteolysis with pronase.

Plasmodium falciparum: ingested anti-sporozoite antibodies affect sporogony in Anopheles stephensi mosquitoes.

In endemic areas, malaria-infected mosquitoes may feed upon humans who possess antibodies against malaria sporozoites. Therefore, we examined the effect that ingested anti-sporozoite antibodies have upon Plasmodium falciparum sporogony within Anopheles stephensi mosquitoes. Anti-sporozoite antibodies (IgG) traversed the midgut into the hemocoel within 3 hr following ingestion and, depending upon the titer, persisted for 6-24 hr. When fed to infected A. stephensi at 12 days postinfection (p.i.), anti-sporozoite antibodies bound to sporozoites in the hemocoel, but not to sporozoites residing in the salivary glands of the same mosquitoes. Anti-sporozoite antibodies also bound to developing oocysts when fed to infected A. stephensi at 5 days p.i. Oocysts in mosquitoes that had been fed anti-sporozoite antibodies on Day 5 p.i. produced significantly more sporozoites than did oocysts in nonimmune-fed (Day 5 p.i.) mosquitoes. In addition, the sporozoites from Day 5 immune-fed mosquitoes were significantly more infective to cultured human hepatoma cells than were sporozoites from nonimmune-fed controls. Use of hetereologous immune feedings at Day 5 p.i. did not result in an enhanced production of sporozoites, suggesting that enhancement is related to the specificity of the antibody and is not merely a nutritional effect.