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The macroeconomic effects of tax reform are a subject of significant discussion and controversy. In 2015, the House of Representatives adopted a new “dynamic scoring” rule requiring a point estimate within the budget window of the deficit effect due to the macroeconomic response to certain proposed tax legislation. The revenue estimates provided by the staff of the Joint Committee on Taxation (JCT) for major tax bills often play a critical role in Congressional deliberations and public discussion of those bills. The JCT has long had macroeconomic analytic capability, and in recent years, responding to Congress’ interest in macrodynamic estimates for purposes of scoring legislation, outside think tank groups — notably the Tax Policy Center and the Tax Foundation — have also developed macrodynamic estimation models. The May 2017 National Tax Association (NTA) Spring Symposium brought together the JCT with the Tax Foundation and the Tax Policy Center for a panel discussion regarding their respective macrodynamic estimating approaches. This paper reports on that discussion. Below each organization provides a general description of their macrodynamic modeling methodology and answers five questions posed by the convening authors.

Expansion of forage production acreage for rhizoma peanut (RP - Arachis glabrata Benth.), a persistent perennial, warm-season forage legume adapted to the Gulf Coast region of the southeastern United States, is limited primarily by establishment rate, often taking up to three years. The objective was to determine the effects of two divergent soil environments on the dry matter production and nutrient uptake of RP in the first year following establishment. Five Arachis genotypes, 'Arbrook', 'Florigraze', and experimental lines 423, 575, and 616, were established during March 1995 at Clinton and Olive Branch, LA. Soils were a Dexter silt loam (Ultic Hapludalf) and a Loring silt loam (Typic Fragiudalf, fine-silty, mixed, thermic) with mean pH values of 6.8 and 4.7, respectively. Soils also differed for extractable potassium (K), sodium (Na), calcium (Ca), aluminum (Al), sulfur (S), copper (Cu), iron (Fe), manganese (Mn), and organic matter (OM). Tissue samples were taken at three week intervals in 1996 and yield and quality were evaluated at six week intervals. Locations differed significantly for dry matter production, crude protein (CP), neutral detergent fiber (NDF) and in vitro true digestibility (IVTD). Entries also differed within locations for yield, CP, NDF, acid detergent fiber (ADF), and IVTD. Tissue nitrogen (N), K, Ca, S, Mn, boron (B), and zinc (Zn) were significantly different between locations, but phosphorous (P), magnesium (Mg), Fe, Cu, and Al were not different. Yield and forage quality were both inversely correlated with pH and, with the exception of N, none of the other nutrients were low enough to account for the differences observed in growth between the two locations.

ABSTRACTHuman respiratory syncytial virus (RSV) exists as two antigenic subgroups, A and B, both of which should be represented in a vaccine. The F and G glycoproteins are the major neutralization and protective antigens, and the G protein in particular is highly divergent between the subgroups. The existing system for reverse genetics is based on the A2 strain of RSV subgroup A, and most efforts to develop a live attenuated RSV vaccine have focused on strain A2 or other subgroup A viruses. In the present study, the development of a live attenuated subgroup B component was expedited by the replacement of the F and G glycoproteins of recombinant A2 virus with their counterparts from the RSV subgroup B strain B1. This gene replacement was initially done for wild-type (wt) recombinant A2 virus to create awtAB chimeric virus and then for a series of A2 derivatives which contain various combinations of A2-derived attenuating mutations located in genes other than F and G. ThewtAB virus replicated in cell culture with an efficiency which was comparable to that of the wtA2 and B1 parents. AB viruses containing temperature-sensitive mutations in the A2 background exhibited levels of temperature sensitivity in vitro which were similar to those of A2 viruses bearing the same mutations. In chimpanzees, the replication of the wtAB chimera was intermediate between that of the A2 and B1 wtviruses and was accompanied by moderate rhinorrhea, as previously seen in this species. An AB chimeric virus, rABcp248/404/1030, which was constructed to contain a mixture of attenuating mutations derived from two different biologically attenuated A2 viruses, was highly attenuated in both the upper and lower respiratory tracts of chimpanzees. This attenuated AB chimeric virus was immunogenic and conferred a high level of resistance on chimpanzees to challenge with wtAB virus. The rABcp248/404/1030 chimeric virus is a promising vaccine candidate for RSV subgroup B and will be evaluated next in humans. Furthermore, these results suggest that additional attenuating mutations derived from strain A2 can be inserted into the A2 background of the recombinant chimeric AB virus as necessary to modify the attenuation phenotype in a reasonably predictable manner to achieve an optimal balance between attenuation and immunogenicity in a virus bearing the subgroup B antigenic determinants.

Rhizoma perennial peanut (RPP—Arachis glabrataBenth.) is a high quality, vegetatively propagated, forage legume introduced into southern USA from South America. Information on the performance of seed‐derived lines from this germplasm is lacking. This information is needed to help determine the feasibility of establishing a recurrent selection breeding program to improve the performance of this germplasm. The objectives of this study were to evaluate the variation within Florigraze seedling progeny for reproductive and morphological traits, and to identify lines with superior agronomic characteristics. Three hundred naturally occurring seedlings of Florigraze were identified in the field and characterized for traits including floral initiation, growth habit, leaf morphology, main stem height, lateral growth, and plant density. Seven lines were vegetatively increased for forage evaluation. These lines were evaluated for 2 yr at two locations, for dry matter forage yield, forage quality, plant height, lateral growth, and stand density. None of the Florigraze lines flowered earlier than Florigraze and 22% failed to flower in 3 yr of observation. Means of lines for all morphological traits were consistently below the mean of Florigraze plants. None of the seven replicated lines outperformed Florigraze for all forage traits. Some lines were superior for forage yield or crude protein, but not across locations. If the poor performance of seed‐derived lines from Florigraze is representative of RPP, then future selection and advancement of this germplasm may be seriously limited.

An infectious molecular clone of simian immunodeficiency virus SIVsm was derived from a biological isolate obtained late in disease from an immunodeficient rhesus macaque (E543) with SIV-induced encephalitis. The molecularly cloned virus, SIVsmE543-3, replicated well in macaque peripheral blood mononuclear cells and monocyte-derived macrophages and resisted neutralization by heterologous sera which broadly neutralized genetically diverse SIV variants in vitro. SIVsmE543-3 was infectious and induced AIDS when inoculated intravenously into pig-tailed macaques (Macaca nemestrina). Two of four infected macaques developed no measurable SIV-specific antibody and succumbed to a wasting syndrome and SIV-induced meningoencephalitis by 14 and 33 weeks postinfection. The other two macaques developed antibodies reactive in Western blot and virus neutralization assays. One macaque was sacrificed at 1 year postinoculation, and the survivor has evidence of immunodeficiency, characterized by persistently low CD4 lymphocyte subsets in the peripheral blood. Plasma samples from these latter animals neutralized SIVsmE543-3 but with much lower efficiency than neutralization of other related SIV strains, confirming the difficulty by which this molecularly cloned virus is neutralized in vitro. SIVsmE543-3 will provide a valuable reagent for studying SIV-induced encephalitis, mapping determinants of neutralization, and determining the in vivo significance of resistance to neutralization in vitro.

Simian immunodeficiency virus (SIV) exists within tissues of infected macaques as a mixture of diverse genotypes. The goal of this study was to investigate the biologic significance of this variation in terms of cellular tropism and pathogenicity. PCR was used to amplify and clone 3'-half genomes from the spleen of an immunodeficiency SIV-infected pig-tailed macaque (Macaca nemestrina). Eight infectious clones were generated by ligation of respective 3' clones into a related SIVsm 5' clone, and virus stocks were generated by transient transfection. Four of these viruses were infectious for macaque peripheral blood mononuclear cells (PBMC) or monocyte-derived macrophages (MDM). Three viruses with distinct tropism for macaque PBMC or MDM were tested for in vivo infectivity and pathogenicity. The ability of these three viruses to infect PBMC and macrophages correlated with differences in infectivity and pathogenicity. Thus, a virus that was infectious for both PBMC and MDM was highly infectious for macaques and induced AIDS in half of the inoculated animals. In contrast, virus that was less infectious for PBMC and not infectious for MDM induced only transient viremia. Finally, a virus that was not infectious for either primary cell type did not infect macaques. Chimeric clones exchanging portions of the envelope gene of the 62A and smH4 molecular clones and a series of point mutants were used to map the determinant of tropism to a 60-amino-acid region of gp120 encompassing the V3 analog of SIV. Naturally occurring mutations within this region were critical for determining tropism and, as a result, pathogenicity of these SIVsm clones.

Different patterns of viral replication correlate with the natural history of disease progression in humans and macaques infected with human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), respectively. However, the viral and host factors influencing these patterns of viral replication in vivo are poorly understood. We intensively studied viral replication in macaques receiving identical inocula of SIV. Marked differences in viral replication patterns were apparent within the first week following inoculation, a time prior to the development of measurable specific immune effector responses to viral antigens. Plasma viral RNA levels measured on day 7 postinoculation correlated with levels measured in the postacute phase of infection. Differences in the susceptibility of host cells from different animals to in vitro SIV infection correlated with the permissiveness of the animals for early in vivo viral replication and hence with the postacute set point level of plasma viremia. These results suggest that host factors that exert their effects prior to full development of specific immune responses are critical in establishing the in vivo viral replication pattern and associated clinical course in subjects infected with SIV and, by extension, with HIV-1.

Decline in blood CD4+ lymphocytes during primary symptomatic infections with HIV is usually attributed to viral killing, and has not been considered in terms of altered lymphocyte migration and sequestration. We therefore sought to examine whether CD4+ cell loss from blood of macaques undergoing an acute primary SIV infection might be due to increased synthesis of cytokines, known to profoundly affect lymphocyte trafficking, rather than to direct lymphocyte destruction by virus. The findings indicate that rapid lymphocyte depletion following acute infection is not selective for CD4+ cells, correlates precisely with increased plasma IFN-gamma and tumor necrosis factor-alpha levels, and is reversible. CD4/CD8 ratios in lymph nodes with high viral burdens remain relatively unchanged despite lymphocyte loss from blood. Levels of cytokine mRNA measured in lymphoid organs reflect neither cytokine plasma levels nor their potential to induce sequestration. These results support a model of cytokine-induced lymphocyte extravasation to account for the acute HIV/SIV-induced CD4+ cell lymphopenia and raise questions regarding the extent to which altered lymphocyte migration plays a role in the gradual CD4+ cell depletion throughout infection.

Previous studies suggested that simian immunodeficiency viruses isolated from African green monkeys (SIVagm) are relatively nonpathogenic. The report describes the isolation and biologic and molecular characterization of a pathogenic SIVagm strain derived from a naturally infected African green monkey. This virus induced an AIDS-like syndrome characterized by early viremia, frequent thrombocytopenia, severe lymphoid depletion, opportunistic infections, meningoencephalitis, and death of five of eight macaques within 1 year after infection. An infectious clone derived from this isolate reproduced the immunodeficiency disease in pig-tailed (PT) macaques, providing definitive proof of the etiology of this syndrome. Although the virus was highly pathogenic in PT macaques, no disease was observed in experimentally infected rhesus macaques and African green monkeys despite reproducible infection of the last two species. Whereas infection of PT macaques was associated with a high viral load in plasma, peripheral blood mononuclear cells, and tissues, low-level viremia and infrequent expression in lymph nodes of rhesus macaques and African green monkeys suggest that differences in pathogenicity are associated with the extent of in vivo replication. The availability of a pathogenic molecular clone will provide a useful model for the study of viral and host factors that influence pathogenicity.

The dynamics of plasma viremia were explored in a group of 12 simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta) that had received prior immunization with either nonrecombinant or trivalent (gag-pol, env) SIV-recombinant vaccinia viruses. Three distinct patterns of viral replication observed during and following primary viremia accounted for significant differences in survival times. High-level primary plasma viremia with subsequently increasing viremia was associated with rapid progression to AIDS (n = 2). A high-level primary plasma virus load with a transient decline and subsequent progressive increase in viremia in the post-acute phase of infection was associated with progression to AIDS within a year (n = 6). Low levels of primary plasma viremia followed by sustained restriction of virus replication were associated with maintenance of normal lymphocyte subsets and intact lymphoid architecture (n = 4), reminiscent of the profile observed in human immunodeficiency virus type 1-infected long-term nonprogressors. Three of four macaques that showed this pattern had been immunized with an SIV recombinant derived from the attenuated vaccinia virus, modified vaccinia virus Ankara. These data link the dynamics and extent of virus replication to disease course and suggest that sustained suppression of virus promotes long-term, asymptomatic survival of SIV-infected macaques. These findings also suggest that vaccine modulation of host immunity may have profound beneficial effects on the subsequent disease course, even if sterilizing immunity is not achieved.

The high temperatures, which are often encountered by mine rescue teams during emergency situations, may cause severe physiological strain. For example, at the Somerset coal mine, temperatures of 49°C (120°F) with 100 percent relative humidity caused the normal rescue team recovery mission to be shortened from 2 h to only 25 min. In order to increase the team’s effectiveness and comfort under such conditions, the U. S. Bureau of Mines (USBM) initiated a program with the National Aeronautics and Space Administration (NASA) to develop and test a personal cooling system based on technology developed for the thermal control of space-suited astronauts. The resulting system, which has 88 watt-h (300 Btu) heat absorption capacity, weighs approximately 5 kg (11 lb) and is compatible with existing rescue team breathing apparatus. Several different system configurations were tested under simulated mine rescue team operational conditions of 32.5°C (90°F) wet bulb globe temperature (WBGT) and 1.0 l O2/min (1200 Btu/h) metabolic rate. The system, which consists of a liquid circulation garment and belt-worn heat sink unit, was found to be capable of reducing the physiological strain by nearly 50 percent under these conditions. A simple analytical heat balance model was used to predict the effects of the thermal control system for other environments and metabolic rates. It was found that in the most severe environments, WBGT greater than about 35–37°C, that the maximum endurance time could be further increased by providing an insulating overgarment to reduce the heat gained from the hot environment.

In mice, thymectomized as young adults, neonatally induced tolerance persists in the putative absence of cell chimerism. The finding provides evidence that a selective deficiency of specific clones of lymphocytes exists in transplantation tolerance when induced under the conditions of these experiments.