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OA15.03 I. del Moral Sanchez (1); E.G. Wee (2); S.M. Koekkoek (1); E.E. Schermer (1); W.H. Lee (3); S. Kumar (4); R. Zwolsman (1); J.D. Allen (5); A. Torrents de [...], Background: Soluble immunogens that properly mimic the HIV-1 envelope glycoprotein (Env), such as SOSIP and native flexibly linked (NFL) trimers, are used as constituents for a number of HIV-1 vaccine approaches. However, most NFL and SOSIP constructs are not only expressed as trimers, but also produce undesired monomers and dimers that expose non-neutralizing epitopes. Usually, chromatography procedures are used to isolate the desired trimers for vaccination. However, this also implies that conventional SOSIP and NFL constructs might be less suitable for genetic vaccination. Here, we describe a novel HIV-1 Env construct that was designed to express as trimers only (TO). Methods: First, we combined the TO design with BG505 env to generate a BG505 TO-SOSIP construct as a proof-of-concept. Next, we used TO-SOSIP as a design template to generate a number of different HIV-1 Env immunogens: 1) TO-SOSIP in which immunodominant strain-specific glycan holes were hidden by glycan masking (GM) (TOSOSIP.GM). 2) TO-SOSIP containing germline-targeting (GT) mutations that enable binding by naive precursors of CD4bs broadly neutralizing antibodies (bNAbs) (TO-SOSIP.GT). Results: Transient transfection followed by lectin affinity chromatography showed that the BG505 TO-SOSIP construct expressed only as trimers, of which >85% displayed a native-like conformation, while BG505 SOSIP and NFL-SOSIP preparations contained significant amounts of dimers and monomers. Furthermore, TO-SOSIP interacted efficiently with quaternary dependent bNAbs, such as PGT145 and PGT151, while showing weak binding to most non-NAbs. Both glycan masked and germline targeting variants also expressed only trimers. TO-SOSIPGM showed negligible reactivity to glycan hole-targeting antibodies, while several TO-SOSIPGT variants showed efficient binding to inferred germline versions of several CD4bs bNAbs. Remarkably, the TO design approach also allowed us to generate influenza hemagglutinin (HA) immunogens that express only as trimers without heterologous trimerization domains. Conclusions: The TO design is a useful platform for generating Env and HA immunogens and is especially suitable for genetic vaccination purposes. In the context of DNA prime and protein boost vaccination strategies, the glycan masked and germline targeting TO-SOSIP constructs could prove essential for the early activation of potentially cross-neutralizing epitopes.

An experiment was conducted in market dairy cows to determine the effect of feeding time and ractopamine hydrochloride (RAC) on growth performance, carcass characteristics, and end product quality. In 3 replicates, 9 Holstein cows per replicate (n = 27; 659 [+ or -] 25.3 kg initial BW) culled from 3 dairies were randomly assigned to 3 treatments: 1) slaughter immediately (control), 2) feed for 90 d (NOR), or 3) feed for 90 d with RAC (312 mg.[cow.sup.-1].[d.sup.-1]) for the final 32 d (RAC). On d 0, NoR and RAC cows were placed in individual pens and fed a high concentrate diet (86% concentrate, DM basis) for 90 d before slaughter. All cows were subjectively scored for BCS and locomotion score on d 0, and NoR and RAC cows were evaluated again after 90 d. Individual DMI was recorded daily throughout the trial, and BW was collected every 14 d. Age and age x treatment did not affect (P > 0.05) any of the traits evaluated in this study. When cows fed for 90 d (NoR and RAC combined) were compared with nonfed controls, fed cows had greater (P < 0.001) final BCS, BW and HCW, lower (P < 0.001) final locomo tion score, and greater (P < 0.03) dressing percentage, external fat thickness, and marbling score. Fed cows also tended to have more desirable yield grade (P = 0.08), ribeye area (P = 0.11), fat color (P = 0.09), lean maturity (P = 0.06), and quality grade (P = 0.09) compared with control cows. Warner-Bratzler shear force was not affected (P = 0.23) by feeding. However, a 12-member trained sensory panel revealed that fed cow carcasses had more desirable (P < 0.04) tenderness, juiciness, and overall acceptability than control cow carcasses. Flavor intensity also tended (P = 0.10) to be more desirable for fed vs. control cows. No difference (P > 0.10) in off-flavor was detected among treatments. Finally, there was no effect (P > 0.10) of RAC on growth performance, carcass characteristics, or end product quality. In conclusion, feeding a high concentrate diet for 90 d improved important live animal, carcass, and end product characteristics related to the quality and palatability of beef from market dairy cows; however, no effect of RAC supplementation was observed. Key words: carcass quality, end product, growth performance, market dairy cow, preslaughter feeding, ractopamine hydrochloride

In free-spawning marine invertebrates, larval development typically proceeds by one of two common modes: planktotrophy (obligate feeding) or lecithotrophy (obligate non-feeding). In a rare third developmental mode, facultative planktotrophy, larvae can feed but do not require particulate food to complete metamorphosis. Facultative planktotrophy is thought to be an intermediate strategy that results evolutionarily from an increase in the energy content of the egg. We tested the hypothesis that a decrease in egg energy content is sufficient to shift development from facultative to obligate planktotrophy by experimentally reducing the egg size of Clypeaster rosaceus, an echinoid echinoderm with facultatively planktotrophic larvae. Blastomeres were left whole (W) or separated at the 2 and 4-cell stage to create half- (H) or quarter-size (Q) 'eggs' from which larvae were reared to metamorphosis, both with and without particulate food. Larvae from all treatments metamorphosed at approximately the same time regardless of food treatment or egg size. In contrast, juveniles that developed from W eggs were significantly larger, had higher organic content, and had longer and more numerous spines than juveniles from H or Q eggs. Larvae from W, H, and Q size eggs were able to reach metamorphosis without feeding, suggesting that the evolution of facultative planktotrophy in C. rosaceus has been accompanied by more than a simple increase in egg size. In addition, our results suggest that resources endogenous to the egg have a larger effect on juvenile size and quality than do exogenous resources such as particulate food.

Empirical data and theoretical models suggest that egg size is an important life history parameter in marine invertebrates. In echinoderms that develop indirectly from small eggs, separating blastomeres at the two-cell stage yields two viable offspring that grow and develop through metamorphosis, although at a smaller size. This observation has led researchers to ask the question: why dont echinoderms produce the smallest eggs capable of development? In laboratory experiments I addressed one potential cost of small egg size: that larvae developing from small eggs suffer increased rates of predation. Blastomeres of the Pacific sand dollar Dendraster excentricus were separated at the two-cell stage and reared to produce halved and full-size sibling larvae. The two larval types were presented simultaneously as potential prey items to five common predators: (1) crab zoea, (2) crab megalopae, (3) chaetognaths, (4) solitary tunicates and (5) postlarval fish. Larvae were tested at several developmental stages ranging from prism larvae through eight-arm plutei. Crab zoea, megalopa, chaetognath and tunicate predators consumed significantly more halved larvae than full-size larvae. Post-larval fish showed the opposite trend, consuming significantly more full-size larvae than halved larvae. For each predator tested, differences in consumption rate were greatest at early developmental stages, when size differences between full and halved larvae were also greatest. These results suggest that the direction of selection on egg size will vary with the presence and abundance of particular predators. Large larvae may reach a refuge from specialists on small prey items but larvae developing from small eggs will reach an equivalent size and be subjected to increased predation rates by specialists on larger prey.