Ability of Emergency Department Physicians Using a Functional Autonomy-Assessing Version of the Triage Risk Screening Tool to Detect Frail Older Patients Who Require Mobile Geriatric Team Consultation

OBJECTIVES

Frailty in older people associates with poor outcomes. Screening by ED physicians would greatly facilitate detection of frail older patients but our previous attempt to introduce routine ED-physician screening with Short Emergency Geriatric Assessment (SEGA), a 13-item frailty tool that French geriatricians use to identify frail patients, failed due to its length and complexity. A national committee recently generated a new version of the fast and simple 5-item Triage Risk Screening Tool (TRST) in which a subjective item ('nurse concern') was replaced by an item assessing basic activities of daily living. The ability of ED physicians using this French-TRST to accurately detect frail patients who require comprehensive geriatric assessment was assessed.

DESIGN

Prospective cross-sectional study on diagnostic accuracy relative to the gold standard, namely, geriatrician-administered SEGA.

SETTING

Tertiary-care hospital, France.

SUBJECTS AND MEASUREMENTS

The participants were 498 ≥75-year-old patients who visited the ED in 2018-2019 and were administered French-TRSTs by first ED physicians and then geriatricians, followed by SEGA, all within 24 hours. Diagnostic accuracy variables were calculated. Geriatrician-TRST was used to identify TRST items that associated with ED physician misclassification of frail patients.

RESULTS

Emergency-TRST was significantly less sensitive than Geriatrician-TRST (88% vs. 93%; p=0.04) and tended to have lower negative predictive value (66% vs. 77%; p=0.09). Emergency-TRSTs rated four French-TRST items less well than Geriatrician-TRSTs.

CONCLUSIONS

As a substitute for SEGA in the ED, the French-TRST performed quite well overall but the ED physicians detected frail patients less well than the geriatricians. Modifications of the French-TRST that may improve the diagnostic performance of ED physicians are discussed.

Vaccine against Helicobacter pylori?

The burden of illness caused by Helicobacter pylori is considerable, and there is little doubt that a therapeutic vaccine would be very useful. However, the merits of using a prophylactic vaccine to eradicate H. pylori from the human population are debatable in light of arguments that it may act as a beneficial commensal organism for many of its human hosts. With regard to the practical side of designing vaccines against H. pylori, animal models have shown us that both therapeutic and prophylactic vaccines are feasible despite the fact that, as in human hosts, immune responses raised naturally to H. pylori cannot eradicate the infection. Many advances have been made in developing optimal vaccination protocols, and recently the first human trial of a therapeutic vaccine, which showed limited but nevertheless encouraging results, was published. However, a possibly quite serious problem is that prophylactic and perhaps also therapeutic vaccines may themselves cause disease.

Human and murine T-cell responses to allelic forms of a malaria circumsporozoite protein epitope support a polyvalent vaccine strategy

Mouse models and a recent vaccine trial have indicated the importance of T-cell immunity to the circumsporozoite protein (CSP) of malaria sporozoites. One of the major impediments for the development of a CSP-based vaccine is that human T-cell epitopes, identified on the CSP, span regions of significant point mutational polymorphism. Studies with human and mouse T-cell clones have indicated that this polymorphism affects T-cell cross-reactivity to Th2R and Th3R, the two most polymorphic and immunodominant epitopes. We extend this observation with polyclonal human T-cell lines, from 11 donors, raised to known variants of Th2R. These lines showed limited but variable cross-reactivity with the heterologous peptides. T cells from B10.A4(R) (I-Ak) mice immunized with each of 18 natural variants of Th2R indicated a similar, limited, cross-reactivity. I-Ak competition assays showed that a number of peptides were unable to bind because of a single polymorphic residue. In both the human and mouse assays, analysis of the sequences of immunogenic cross-reactive and non-cross-reactive peptides suggested that the individual polymorphic residues affect the three-dimensional conformation of the peptide within the major histocompatibility complex (MHC) groove in an, as yet, unpredictable way. These observations argue that design of an epitope able to generate broad cross-reactivity is, to date, not possible. However, despite the limited cross-reactivity of the individual human T-cell lines, most of the donors had T-cell repertoires capable of recognizing all or nearly all of the variants tested, which supports a strategy using a multivalent vaccine.

Life-spans of human T-cell responses to determinants from the circumsporozoite proteins of Plasmodium falciparum and Plasmodium vivax

The longevity of specific human memory T-cell responses is largely unknown. However, a knowledge of the duration of memory is important for understanding immunity to an organism and for planning vaccine intervention. To address this, we have examined T-cell memory to malaria by determining T-cell responses by subjects recently exposed to peptides spanning the circumsporozoite (CS) proteins of two species of malaria-causing organisms, Plasmodium falciparum and Plasmodium vivax. Responses to vivax CS peptides by exposed Thai subjects were more frequent than responses by nonexposed individuals, permitting identification of determinants seen by vivax-induced responses. At the population level, there appears to be life-long memory, as the time since individuals were exposed did not diminish responsiveness to these determinants. In contrast, falciparum-exposed subjects were largely indistinguishable from nonexposed controls in responsiveness to falciparum CS determinants. However, a single peptide (F16: DNEKLRKPKHKKLKQPGDGN) was recognized significantly more frequently by P. falciparum-exposed than nonexposed Thai subjects. T cells responsive to this peptide were CD450+ and produced gamma-interferon. In contrast to the response to the vivax determinants and the other falciparum determinants, responsiveness to F16 was undetectable or minimal 2 years after exposure. Our data provide the average life-spans of certain malaria-specific T cells and are consistent with, but do not prove, the hypothesis that antigenic persistence (in the form of P. vivax hypnozoites) correlates with persistence of human T-cell memory.

Natural amino acid polymorphisms of the circumsporozoite protein of Plasmodium falciparum abrogate specific human CD4+ T cell responsiveness

Sequence polymorphism has been reported for virtually all malaria antigens and, in the case of the circumsporozoite (CS) protein, this variation is in the form of point mutations concentrated primarily in several regions recognized by T cells. The factors responsible for the variation are unknown. We studied the T cell responses to all known variants in malaria-exposed Thais. Memory CD4+ T cells responded to variants of a polymorphic immunodominant region (denoted Th2R), and CD4+ T cell clones specific for one Thai Th2R variant were generated. There was minimal cross-reactivity to any of the naturally occurring variants, including the other Thai variant, and competition studies performed with the clones using analog peptides demonstrated that all the substitutions of the polymorphic residues modulate either the binding of the peptide to major histocompatibility complex (MHC) molecules or the recognition by the T cell receptor of the peptide-MHC complex. Our data suggest that CD4+ T cells may be able to select parasites expressing variant sequences and have implications for development of a CS-based vaccine.

'Original antigenic sin', T cell memory, and malaria sporozoite immunity: an hypothesis for immune evasion

Prior to any exposure to malaria, most adults have T cells specific for malaria parasites and various malaria proteins. The protein for which this has been shown more than any other is the circumsporozoite protein (CSP) of Plasmodium falciparum. These T cells can be present in high frequency and appear to have arisen through exposure to other (non-malaria) organisms. Although T cells are thought to provide protection against sporozoites, these T cells specific for cross-reactive organisms are clearly unable to protect against malaria, and may be preferentially expanded following exposure to malaria sporozoites. Thus, cross-reactive organisms have the potential to skew the repertoire of sporozoite-induced T cells and affect the induction of protective immunity. This is analogous to the concept of 'original antigenic sin' whereby prior exposure to one strain of influenza virus was shown to be able to divert the antibody response to a second challenging strain to focus on the shared (cross-reactive) epitopes.

High frequency of malaria-specific T cells in non-exposed humans

A major goal of current candidate malaria vaccines is to stimulate the expansion of clones of malaria-specific lymphocytes. We have examined the in vitro T cell responses of a group of malaria exposed and non-exposed adult Caucasian donors to recombinant circumsporozoite (CS) proteins, one of which is undergoing clinical trials, to blood-stage parasites, and to synthetic peptides copying the CS protein and defined blood-stage proteins. In nearly all individuals tested, CD4 T cell proliferation or lymphokine production occurred in response to whole parasite or CS protein stimulation, and T cells from many individuals responded to synthetic peptides. T cell responses were major histocompatibility complex-restricted, and stimulation of T cells with malaria parasites or CS protein did not appear to expand a population of T cell receptor gamma/delta cells. Malaria-specific responses were independent of prior malaria exposure, and in some cases exceeded the magnitude of response to tetanus toxoid. Specific T cells are present in high frequency in the peripheral blood of many donors who have never been exposed to malaria. Although malaria-specific CD4 T cells play an important role in immunity, these data question whether vaccines need to stimulate such cells, and focus attention on other aspects of malaria immunity which may be more critical to a successful vaccine.

Peptide analysis of the T cell response to the malaria circumsporozoite (CS) protein

The T cell response to the circumsporozoite (CS) protein is still not well understood. There is still not agreement on the degree of immunological non-responsiveness or even on the basic question of whether the response to native CS protein requires T cells at all. Recombinant proteins and synthetic peptides are tools that are helping us learn the basics of the immune response to this protein. Here, the human and murine responses to the protein are probed using these valuable research tools. Then, the possibility of using peptide vaccines is discussed.

Major population differences in T cell response to a malaria sporozoite vaccine candidate

Using a complete series of overlapping peptides, we have identified the T cell epitopes of a malaria vaccine candidate, the circumsporozoite (CS) protein, that are recognized by sporozoite-exposed residents of a non-endemic country. This protein and subunits from it are being considered as malaria sporozoite vaccine candidates, as CS-specific antibodies and cytotoxic T lymphocytes have been shown to have a role in protection. The rationale for developing an antibody-based vaccine is that in Plasmodium falciparum the immunodominant B cell epitope of the protein, (Asn-Ala-Asn-Pro)n [(NANP)n], is invariant. However, the ideal vaccine must contain CS protein-derived T cell antigenic epitopes to allow natural boosting of the antibody response following sporozoite exposure. Here, we show that major differences occur between the CS-specific T cell responses of non-endemic Caucasians and an endemic African population. HLA differences between the populations are, in part, responsible. Subunit malaria vaccines for one population may be ineffective in a different population.